WO2010004416A2

WO2010004416A2 - Method and relative apparatus for carrying out diagnostic analyses

Info

Publication number: WO2010004416A2
Application number: PCT/IB2009/006201
Authority: WO
Inventors: Paolo Galiano; Giovanni Di Cola; Francesco Frappa
Original assignee: Alifax Holding SpA
Current assignee: Alifax SRL
Priority date: 2008-07-08
Filing date: 2009-07-07
Publication date: 2010-01-14
Anticipated expiration: 2011-01-08
Also published as: ITUD20080162A1; WO2010004416A3

Abstract

Method for diagnostic analyses of a biological sample, comprising: - a step of preparing a mixture of a biological sample and one or more reactive agents, - a step of reaction of the antigen-antibody type, wherein the one or more reactive agents react in the mixture with one or more components of the biological sample according to a reaction kinetics. The method also comprises a step of measuring the initial speed at which the reaction occurs, and a step of comparing at least part of the reaction kinetics with standard kinetics having a known concentration, corresponding to a reaction of the same type as that to which the biological sample is subjected, so as verify if the initial concentration of antigen or antibody is greater than the concentration of the reference standard, in order to obtain an indication as to whether the biological sample is affected or not by the prozone effect.

Description

"METHOD AND RELATIVE APPARATUS FOR CARRYING OUT DIAGNOSTIC ANALYSES" ψ φ ^! ψ φ

FIELD OF THE INVENTION The present invention refers to a method and the relative apparatus for carrying out diagnostic analyses in which the error of measurement due to the so- called "prozone effect" are taken into account, usable in the field of laboratory tests and/or analyses.

The present invention is applied preferably, but not only, to detect the prozone effect in an immunological reaction of the antigen-antibody type on a biological sample to detect possible pathologies or other.

BACKGROUND OF THE INVENTION

It is known that some diagnostic tests, carried out on the serum of a patient and based on antigen-antibody reactions, are sometimes affected by errors of measurement, due to the excessive quantity of antigen or antibody which is to be measured in the serum of a patient.

This phenomenon has been known for a long time and has been defined or called "prozone effect". For a description of this effect see, for example, Michael Heidelberger, Forrest E. Kendall, "The precipiting reaction between type III pneumococcus polysaccharide and homolgous antibody" and "The Michael Heidelberger Papers, Antigens and Antibodies: Heidelberger and the rise of quantitative immunochemistry, 1928, 1954, on the internet site http://piOfiles,nlm.nih.gov/DH/Views/Exhibit/narrative/immunochemistry.html.

The excessive quantity of an antigen or antibody to be detected in the serum of a patient in prozone effect gives an erroneous low result, or rather the antigen- antibody system of the biochemical reaction measurable in the test tube, or in the measuring container, "collapses" and expresses a false negative result, even when testing samples of patients clearly affected by the pathologies which the measurement is intended to test. It is obvious that being able to recognize a falsely positive sample in advance, following the prozone condition, means avoiding a misclassification of the diagnosis, and therefore avoid a mistake with respect to a clinical diagnosis. Moreover, it also means simplifying procedures for possibly challenging data, in that it allows to automatically repeat the sample where the prozone effect has been recognized, and therefore the laboratory procedures themselves are simplified.

The main problems of the prozone effect, also called matrix effect, are, as we said, the reporting of negative samples which are instead positive. Normally, this "prozone" effect is recognized by a case history that is not consistent with the examination obtained and the diagnosis is normalized following other considerations or clinical analyses. The delay causes a reconsideration of the sample through a dilution of the serum under examination, so as to make it come within an optimization of the antigen- antibody concentrations in order to overcome the "prozone" effect, in practice carrying out a second and third repetition of the sample.

This determines an inevitable increase in the analysis times and, therefore, the times of obtaining the diagnostic result, which, in the case of "mass" exams carried out in clinical laboratories in hospitals or elsewhere, determines an increase in waiting times for the application of suitable therapies.

In particular, document EP-A- 1.845.373 is known, which provides an immunological assay which allows to calculate the concentration of analyte in a sample in which the prozone effect has been verified, by means of a signal detected at the end of the immunological reaction.

Moreover, the document Papik K et al. "Automated Prozone Effect Detection in Ferritin Homogenous Immunoassays Using Neural Network Classifiers" describes a method for recognizing the prozone effect in an assay for the determination of ferritin, by means of analyses of a reaction kinetics after the measurement. The method uses a trained neural network based on 77 samples from 48 patients to filter the false-negative results immediately after their determination. In particular this document provides a temporal analysis, at the end of the reaction, by using a plurality of curves of the reaction kinetics of samples affected by the prozone effect. The method described in the Papik K. et al. document is disadvantageous and complex in that it requires the predisposition of numerous external control parameters, represented by the 77 standard samples affected by prozone used for training the neural network. The control parameters are maintained constant and unchangeable over time inside the measurement system. The presence of these external samples can constrain the reliability of the detection to the temperature range at which the standard samples have been considered, just as one can find a great influence of the immunological mechanisms which occur in the course of the reaction, when compared with the standard samples, and the volume measurements of reagents used. One therefore has limits connected to the lack of adaptability to variations that the system can have, such as temperature, change in volume of the reagents, different batch of reagents, change in the timing of the analyses.

The document Ermens et al. "Dilution Protocols for Detection of Hook Effects/Prozone Phenomenon" is also known, which describes a dilution protocol to detect the prozone effect in a sample.

Finally, the document Hoffman K. L. et al. "Elimination of Hook-Effect" in Two-Site Immunoradiometric Assays by Kinetic Rate Analysis" describes a method to eliminate the prozone effect in immunoradiometric assays (IRMA) to detect human choriogonadotropin (hCG), by screening the reaction kinetics. The screening is carried out by monitoring the simultaneous incubation of the solid phase and the antibody at 2 minutes from the onset of the reaction and at 10 minutes, when the reaction is complete.

In general, all the prior art documents cited above provide the "end-point" type of analyses, that is, analyses carried out at the end of the reaction, with the main disadvantage of increasing the waiting times and the reporting times in cases where the prozone effect is manifested, at the end of the analysis.

One purpose of the present invention is to perfect a method for carrying out diagnostic analyses which aims to detect a prozone effect, in clinical analyses and/or diagnostic tests, overcoming the shortcomings of the state of the art, and which allows to reduce the detection times.

A further purpose of the present invention is to create an apparatus for diagnostic analyses which allows to reduce the detection times of a prozone effect, advantageously ending the reaction in advance once the possibility has been detected that the sample under analysis is affected by the prozone effect, to safeguard the patient, thus avoiding a mistaken diagnosis in reference to the potential error determinate by the matrix or "prozone" effect, and to reduce the overall costs of the analyses and/or diagnostic tests, and in which the analysis is - A -

not constrained to parameters, such as the temperature for example, at which the standard reference samples have been considered.

The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.

SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independent claims, while the dependent claims describe other characteristics of the invention or variants to the main inventive idea. In accordance with the above purposes, a method of diagnostic analyses with the detection of a prozone effect according to the present invention is usable for laboratory tests and analyses on a biological sample.

The method according to the present invention provides a preparation step to prepare a mixture of the biological sample to be analyzed and one or more reactive agents, the preparation of the mixture being carried out, for example, inside a chamber at a controlled temperature.

Each of the reactive agents is specific for a determinate analysis to be carried out on the biological sample.

The reactive agents are supplied in one or more batches and each batch comprises a plurality of standard reference samples of the same reactive agent at different concentrations. Moreover, in each batch there is a determinate reference sample of a reactive agent having a greater concentration with respect to the concentration of the other agents or reactive samples comprised in the same batch. Each batch of samples comprises, or is associated with, its own calibration or setting curve, normally optic absorbance (or delta absorbance) versus sample concentration, formed by a series of points, for example six, each relating to a sample with a different concentration, and therefore each associated with its own different reaction kinetics curve. One of the points which make up the calibration or setting curve is the point of the sample with the highest concentration, and therefore represents the final point of the calibration curve. Normally the calibration or setting curve is used to correlate the experimental values detected, for example absorbance, relating to the biological sample examined with the relative concentration of analyte to be measured.

The maximum concentration value of the reference sample represents a threshold limit of concentration beyond which the prozone effect is found for the determinate reactive agent. Each batch is supplied with an index of initial speed of the reaction kinetics of the agent or sample with the highest concentration, expressed as a slope of the relative line tangent to an initial point of the curve of the reaction kinetics of the sample with the highest concentration.

The reactive agent used can be, for example, an antibody or an antigen for a determinate analyte to be quantified in the biological sample, and may be, for example, made up of particles of latex or of colloidal gold, sensitized with a specific antibody or antigen (agglutination reaction) or with an analysis of the aggregation kinetics of a mass.

Said preparation step can also advantageously provide a mixing step with relative homogenization to assist the meeting between the analyte and reactive agents.

The present invention also provides a reaction step of the antigen-antibody type, in which one or more reactive agents react in the mixture with one or more components of the biological sample according to a curve representative of the reaction kinetics.

The method then comprises a step of measuring the initial speed at which the said reaction between the biological sample and the selected reactive agent occurs. The measuring step is carried out at the same time and in a dynamic way with respect to the progress of the reaction step. The measuring step is carried out by evaluating the slope of a line tangent to an initial point of the curve of the reaction kinetics of the biological sample. The measuring step, in particular, is carried out instantly after the mixing. Typically, the reaction kinetics is to a large extent dependent on the initial concentration of the components of the biological sample and/or on the temperature of the mixture obtained in the mixing step, on the type of biological sample and the reactive agent used and on the degree of mixing.

The present invention also provides a step of comparing the initial reaction speed of the biological sample, represented by a speed index expressed by the slope of the relative line tangent to the initial point of the curve of the reaction kinetics of the biological sample, and the speed of the initial reaction of the standard reactive agent with the greater concentration, represented by said speed index expressed by the slope of the reference line tangent to the curve of the reaction kinetics for the sample with the greater concentration, to verify if the initial concentration of antigen or antibody is greater than the concentration of the reference standard with the greater concentration, with the purpose of detecting in advance, before the end of the reaction step, any prozone effect in the biological sample analyzed. According to one form of embodiment of the present invention, the technique of photometric measuring or reading is used to measure the reaction kinetics, in order to determine the concentration of the mixture present inside the measuring chamber. The measuring is of the kinetic type, and able to detect variations in optic density over time, with the frequency and number of measurements variable according to the type of reaction to be detected.

The reaction kinetics, corresponding to the reaction which is effectively carried out on the biological sample tested, is compared to a series of standard kinetics obtained with a known concentration of specific analyte. The concentrations of analyte of said standards comes within the concentrations not affected by prozone effect. The measuring of the reaction kinetics of the sample tested is carried out for every point of the standards that make up the calibration curve.

The standard with the greater concentration of analyte is near to the limit point at which the prozone effect manifests itself, so that one obtains a limit relating to the sample tested beyond which there is a high probability that there is a prozone effect in said sample.

The present invention discriminates between samples which are affected and not affected by the prozone effect in a dynamic way, that is in real time, inasmuch as it follows the progress of the reaction reading the experimental datum, for example the value of absorbance, with high frequency of sampling, deciding whether to abort the measure with excessive speed already in the first phase of the reaction, thus obtaining in advance the information on whether the biological sample tested is affected by the prozone effect, before the end of the reaction.

With the present invention it is possible to supply a re-mapping of the fundamental parameters for functioning with each batch of reactive agents which are used, thanks to the calibration curve which is supplied with each batch. Advantageously, since the present invention measures the initial step of the reaction kinetics without comparable fixed references of kinetics, that is the prozone standards used in the state of the art, this is not constrained, in its adaptability and reliability, to the conditions with which the standard reference samples affected by prozone effect have been assessed, such as temperature, volumetry of the reactive agent or other.

Consequently, the present invention is not constrained to standards which have a prozone effect of the fixed or pre- calibrated type, since the prozone effect reference used is measured dynamically during the course of the analysis of the reaction at maximum concentration. The invention, therefore, does not need a plurality of external control parameters, rather it studies and measures the kinetic progress of a standard which is part of the reference reaction curve itself. It thus overcomes the disadvantages of the state of the art, since the serologic types of the prozone standard known in the state of the art cannot be the same as an unknown sample which shows intrinsic kinetics at the moment the analysis is in course.

In a perfected version of the present invention, during the detection of the value of the calibration standards, the system memorizes the progress of the kinetic reaction curves, detected for the individual points that make up the calibration curve, extrapolating, from the kinetic curve with the highest concentration of analyte, the derivative of the first reaction phases, as the index of speed with which this kinetic develops.

The value of this index, or slope of the curve in the first reaction phase, is memorized, and used afterwards, as a comparison value for the detection of samples affected by the prozone effect. In other words, the sample is affected by prozone if the speed of the initial reaction is greater than that of the standard with the greater concentration, and considered as a threshold value for the prozone effect. The speed of initial reaction of the sample affected by prozone is measured as a slope referred to the reference curve of the standard with the greater concentration and therefore, the comparison of the aggregation slope reveals, if one finds an anomalous slope greater than the slope of the calibration curve, the possible presence of the prozone effect in the sample tested. With the present invention, it is therefore possible to identify automatically and in advance, with respect to the normal evolution times of a reaction, a biological sample subject to prozone effect, so as to allow to dilute the sample and proceed to a subsequent analysis of the diluted sample without running the risk of falsely negative results. According to one embodiment of the present invention, but not limited only to this methodology, the measuring is applied to reactions using particles of latex sensitized with a specific antibody or particles of latex sensitized with the specific antigens of the analyte that is to be quantified.

The present invention also refers to an analysis apparatus to analyze biological samples and at the same time detect a possible prozone effect in said samples.

The apparatus according to the present invention comprises a mixing chamber suitable to contain and to mix a biological sample to be analyzed and one or more reactive agents.

The apparatus comprises a measuring chamber, advantageously at a controlled temperature, and measuring means associated with the measuring chamber and suitable to detect the chemical and/or physical parameters of the reaction, including the evaluation of the slope of a line tangent to an initial point of the curve of the reaction kinetics of the biological sample.

Processing and control means are also provided, comprising memorization means in which, for each of said batches, the reaction speed index is memorized in its initial phase for the reactive agent with the greater concentration comprised in the calibration curve of the device. The index expresses at least the initial reaction speed of the respective reactive agent as a slope of the relative reference line tangent to the initial point of the curve of the reaction kinetics of the sample with the greater concentration.

According to a characteristic feature of the present invention, the measuring chamber is directly associated with the mixing chamber to allow an immediate, or almost immediate transfer of at least part of the biological sample mixed by the mixing chamber to the measuring chamber at the beginning of the reaction of the reactive agent with the biological sample.

The measuring, therefore, is carried out at the same time and in a dynamic way with respect to the progress of the reaction in the mixing chamber. Moreover, said measuring is carried out by means of the evaluation, by said processing and control means, of the slope of a line tangent to the initial point of the reaction kinetics of the biological sample and the comparison of the initial speed of reaction of the biological sample, represented by the slope of said tangent line and the initial reaction speed of the standard reactive agent with the greater concentration, represented by the slope of said reference tangent line, so as to detect in advance, before the end of the reaction in the mixing chamber, a possible prozone effect in the biological sample analyzed.

This allows to measure the initial reaction kinetics of the biological sample in order to compare the initial speed of the reaction kinetics with the initial speed of the reaction kinetics of the standard with the greater concentration; if a greater reaction speed occurs in advance before the evolution of the reaction of said higher standard, a biological sample affected by prozone effect is thus identified with the method described above.

According to a variant of the present invention the apparatus also comprises, dispensing means of the microvolumetric type suitable to deliver said reactive agent and/or the biological sample in microvolumetric quantities into the mixing chamber in order to modify in a controlled way the concentration of the biological sample itself.

There is also a variant of the present invention which provides that the device comprises electronic processing and control means, associated both with the measuring means and also with the dispensing means, and suitable to control the dispensing means for the controlled delivery of the reactive agent and/or the biological sample into the mixing chamber according to the detection carried out by the measuring means. BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the present invention will become apparent from the following description of a preferential form of embodiment, given as a non-restrictive example with reference to the attached drawings wherein: - fig. 1 is a schematic illustration of an apparatus for analyses according to the present invention;

- fig. 2 is a temporal diagram which illustrates different kinetic reaction speeds in a method according to the present invention. DETAILED DESCRIPTION OF A PREFERENTIAL FORM OF

EMBODIMENT

With reference to the attached drawings, a method and the relative apparatus

10 for carrying out diagnostic analyses with the detection of a prozone effect, according to the present invention, are used on a biological sample, such as for example plasma or serum, of a patient. Such analyses provide a chemical and/or physical reaction between the biological sample and one or more reagents.

The method and relative apparatus 10 are usable, for example, in analyses on a biological sample which provide a reaction of the antigen-antibody type, in which a certain quantity of antibody or antigen is attached on a carrier typically comprising polystyrene balls, with an average diameter of about 0.12 microns (sensitized latex), or particles of colloidal gold, to activate an agglutination reaction. The reaction has a kinetics dependant for the most part on the biological sample itself, on its temperature, on its concentration and on its mixing.

The apparatus 10 comprises a mixing chamber 14 suitable to contain the biological sample, and a measuring chamber 11 directly connected to a mixing chamber 14, in which a series of pre-defined measurements are carried out on the biological sample. The apparatus 10 also comprises one or more dispensers 17 of the microvolumetric type, connected to the mixing chamber 14, and suitable for the controlled delivery of at least one reactive agent to the biological sample already present in the mixing chamber 14.

The present invention provides to supply one or more batches of reactive agents, each of which is specific and adapted for the analysis or assay to be carried out. Each batch comprises a plurality of standard samples of the same reactive agent, at different concentrations. Among the reactive agents of the same batch, there is a determinate sample of reactive agent with the greater concentration. The greater concentration represents a threshold limit beyond which the reactive agent of the batch considered has a prozone effect.

Each batch is also supplied with a kinetic calibration or setting curve, associated with the reactive agent in question, to correlate the absorbance values detected to the concentration of analyte tested. The correlation curve consists of N points of increasing concentration, not, however, affected by the prozone effect, and the last point, with the greater concentration, has a concentration near to the prozone effect. At every reactive change a new calibration curve is thus supplied.

A reaction speed index is also supplied, which is represented by the slope of the line (line s in fig.2) tangent to the initial point of the curve C in fig.2, which expresses the reaction kinetics of the component with the greater concentration, and represents the initial reaction speed for the standard with the greater concentration of the determinate batch of reactive agents.

The present invention, therefore, supplies to the system of analysis the calibration curve made by measuring, for example, six samples with a known concentration of analyte, distributed in the range of concentrations not affected by the prozone effect, plus the value of the derivative (slope) of the reaction kinetics with the greater concentration, which will be used as a discriminator for samples affected by prozone effect. The derivative is made on the first seconds of reaction supplying a speed index unconstrained by the measurements of volume of reagents contributing to the reaction and provides neither the integral calculation nor the comparison of the kinetics analyzed with sample kinetics memorized and unchangeable over time.

The apparatus 10 also comprises a photometric measuring device associated with the measuring chamber 11. The photometric measuring device comprises an emitter of a luminous radiation 12 and a diffuser 16, associated with the emitter 12 and suitable to diffuse the luminous radiation inside the measuring chamber 11.

The apparatus 10 also comprises a photometric sensor 13, associated with the measuring chamber 11 and suitable to detect the intensity of luminous radiation that passes through the measuring chamber 11, for example in terms of optical absorbance, and a processing and control unit 40, connected both to the photometric sensor 13 and to the dispensers 17. The processing and control unit 40 comprises memorization means 42 in which, for each of said batches of reactive agents, the relative setting or calibration curves and the relative slopes of the lines tangent to the initial point of each curve (standard with the greater concentration) are memorized as the expression of the initial speed index of the reaction.

The method provides a preparation step in which the biological sample tested, or part of it, is put inside the mixing chamber 14 by means of an injector 18 connected to the mixing chamber itself. Sensitized latex is added to the biological sample contained in the mixing chamber 14, in order to activate said reaction with the antigens or antibodies contained in the biological sample. The sensitized latex is delivered in a controlled way into the mixing chamber 14 by means of the dispensers 17, adding predefined quantities having a range of size equal to the microvolumes.

The method then comprises a mixing step in which the sensitized latex is mixed with said part of the biological sample. The mixing of the biological sample in the mixing chamber 14 is carried out in a known manner, for example using mechanical stirrers disposed inside the mixing chamber 14 and not shown in the attached drawings, or an ultra-sound system applied outside the mixing chamber 14.

There is then a reaction step in which the sensitized latex reacts with the biological sample contained in the mixing chamber 14. The reaction develops with a reaction kinetics depending on the concentration of analyte present in the biological sample, on the temperature of the mixture, on the type of biological sample and on the reactive agent used and on its mixing.

The method also comprises a step to detect the speed of the reaction between the biological sample and reactive in its initial stage. A part of the mixed biological sample present in the mixing chamber 14 is, therefore, conveyed forcedly into the measuring chamber 11 to carry out a first detection of the concentration effected in a known manner by means of the luminous source emitter 12 and the associated photometric sensor 13.

The speed of initial reaction of the sample mixed with the reactive agent, or slope of the reaction kinetics in its initial part, is compared to the speed of the reference initial reaction, deduced from the reference standard indicative of a reaction corresponding to the same type of biological sample in the same conditions as the biological sample tested and not affected by prozone effect. In particular, if the standard compared is that with the greater concentration, when the speed of the reaction of the biological sample is greater than that of the standard, this is an indication of the presence of prozone effect.

As mentioned above, fig. 2 illustrates the temporal graph in which the curve C shows the temporal development of the reaction kinetics, that is of the variation of the concentration over time, indicative of the said reference standard. In this case the measuring of the initial kinetics of the biological sample tested is carried out by measuring the initial variation of the concentration in correspondence with an initial condition defined by the concentration A in the instant tl, identical to that of the reference standard of the curve C. This measurement is carried out in a known way by means of the processing and control unit 40 and one or more measurements detected by the photometric sensor 13.

The initial reaction kinetics is compared to the standard reference kinetics. In this case the initial reaction kinetics of the sample is represented by the slope of the line r which is compared with the slope of the reference kinetic curve and represented by the line s tangent to the curve C again corresponding to the instant tl .

If the initial kinetics detected by means of the photometric sensor 13 is greater than the reference kinetics in the same instant tl, that is if the line r has a greater slope than the slope of the line s, this is an indication that the biological sample is, most probably, affected by the prozone effect, inasmuch as this situation is indicative of a concentration higher than the limit measurement. This is essentially due to an excess of antigen or antibody in the biological sample tested. In this way it is possible to identify in advance if a biological sample is affected or not by the prozone effect so as to stop the analysis in progress and to repeat it in due course, taking another portion of the biological sample. This reduces the time needed for carrying out the diagnostic analysis, detecting and discarding in advance any possible unreliable analyses. The connection and the proximity of the mixing chamber 14 and the measuring chamber 11 allow the quick transfer of a portion of the biological sample in order to calculate in a precise way the initial reaction kinetics and detect beforehand a possible prozone effect in the sample tested, before the end of the reaction itself. Moreover the delivery in microvolumetric quantities of the sensitized latex, that is of the reactive agent in the mixing chamber, allows to correct/modify the dilution of the sample itself. In fact if the biological sample is identified as subject to prozone effect, then the processing and control unit 40 empties the measuring chamber 11 and prepares a new analytic session of the diluted biological sample, bringing its concentration further within the measurement limits.

If, on the other hand, the initial development speed of the kinetics detected is lower than that of the reference speed in the same instant tl, a condition for instance shown in fig. 2 by the line t, having a lesser slope than that of the line s, then this condition is indicative of a biological sample not affected by prozone effect, since its concentration comes within the measurement limit. In this case the reaction step of the biological sample mixed in the mixing chamber 14 is left to proceed to its end. The method also comprises an analysis step of the mixed biological sample, in which the reacted biological sample is transferred from the mixing chamber 14 to the measuring chamber 11 and is analyzed in a known way by means of the photometric sensor 13 to detect the parameters of the reaction necessary to identify the pathologies of the patient from whom the biological sample came. The speed of analysis of the reaction plays a fundamental part, since the present invention reduces all the times between the addition of the reagent/s and the reading of the reaction kinetics for the mechanical conformation of the measuring chamber 11 which is positioned immediately under the mixing chamber 14. Sampling the reaction at a speed of one reading per second (sampling frequency), the present invention is able to determine in an accurate way the first step of reaction, ending the reaction itself if this has, in the initial step, a reaction speed higher than that provided as a reference. Contrary to the state of the art, the present invention uses considerably reduced reactions in terms of time, inasmuch as the reaction lasts only about 60 seconds. It is clear that modifications and/or additions of parts and/or steps may be made to the apparatus for carrying out diagnostic analyses as described heretofore, without departing from the field and scope of the present invention.

Claims

1. Method for diagnostic analyses of a biological sample, comprising:

- a step of preparing a mixture of a biological sample and one or more reactive agents, - a step of reaction of the antigen-antibody type, wherein the one or more reactive agents react in the mixture with one or more components of the biological sample according to a reaction kinetics curve, characterized in that each of said reactive agents is specific for a determinate analysis to be made on the biological sample, said reactive agents being supplied in one or more batches, each batch comprising a plurality of standard reference samples of the same reactive agent at different concentrations, amongst which a determinate sample of reactive agent has a greater concentration than the concentration of the other reactive agents comprised in the same batch, the value of maximum concentration of said determinate sample of reactive agent representing a threshold limit of concentration beyond which the prozone effect is found for the determinate reactive agent, each batch being supplied with an index of initial speed of the reaction kinetics of the sample with the greater concentration, expressed as a slope of the relative line (s) tangent to an initial point of the reaction kinetics curve of the sample with the greater concentration, and in that said method also comprises:

- a step of measuring the initial speed at which said reaction occurs, said measuring step being carried out simultaneously and dynamically with respect to the progress of said reaction step, said measuring step being carried out by evaluating the slope of a line (r, t) tangent to an initial point of the reaction kinetics curve of the biological sample, and

- a step of comparing the initial reaction speed of the biological sample, represented by the slope of said line (r, t) and the initial reaction speed of the standard reactive agent with greater concentration, represented by the slope of said line (s), so as verify if the initial concentration of antigen or antibody is greater than the greater concentration of the reference standard, in order to detect in advance, before the end of said reaction step, a possible prozone effect in the biological sample analyzed.

2. Method as in claim 1, characterized in that if the initial reaction speed of the biological sample is greater than the initial reaction speed of the standard, this is an indication of high probability of the presence of a prozone effect.

3. Method as in claim 1, characterized in that said step of measuring the speed of reaction is performed using the technique of photometric reading for measuring the variation over time of the optical density.

4. Method as in claim 1 or 2, characterized in that it provides at least a mixing step of the biological sample and said one or more reagents.

5. Method as in any claim hereinbefore, characterized in that said measurement of the reaction kinetics of the biological sample under examination is performed for every point of the standards that define the comparison curves.

6. Method as in any claim hereinbefore, characterized in that during a step to detect the value of the calibration standards, it provides to memorize the development of the kinetic curves of reaction, extrapolating, from the kinetic curve having the greater concentration of analyte, the derivative of the first reaction steps as an index of speed at which this kinetics develops, the value of said index, or slope of the curve in the first reaction step, being memorized and used as a value of comparison for detecting samples affected by the prozone effect.

7. Method as in any claim hereinbefore, characterized in that it also comprises a step in which a biological sample detected as being affected by the prozone effect is suitably diluted before the subsequent analysis is carried out.

8. Method as in any claim hereinbefore, characterized in that as reactive agent particles of latex are used, or of colloidal gold, sensitized with a specific antibody or antigen, or the kinetics of aggregation of a mass is analyzed.

9. Apparatus for diagnostic analyses of biological samples comprising:

- a mixing chamber (14) able to mix a biological sample with one or more reactive agents able to react with one or more elements or components of the biological sample,

- a measuring chamber (11) able to perform one or more measurements on said biological sample mixed with the reactive agent,

- measuring means (13) associated with the measuring chamber (11) and suitable to detect a predetermined set of chemical and/or physical parameters, correlated to said one or more components of the biological sample, indicative of said reaction, characterized in that:

- said reactive agents are supplied in one or more batches, each batch comprising a plurality of Standard reference samples of the same reactive agent at different concentrations, amongst which a determinate sample of reactive agent has a greater concentration than the concentration of the other reactive agents comprised in the same batch, the value of maximum concentration of said determinate sample of reactive agent representing a threshold limit of concentration beyond which the prozone effect is found for the determinate reactive agent,

- the measuring means (13) are able to evaluate the slope of a line (r, t) tangent to an initial point of the reaction kinetics curve of the biological sample, said apparatus also comprising:

- processing and control means (40) comprising memorization means (42) in which is memorized, for each of said batches, at least an index of the reaction speed in its initial phase for the reactive agent with the greater concentration, said index expressing the initial reaction speed of the respective reactive agent as the slope of the relative line (s) tangent to the initial point of the reaction kinetics curve of the sample with the greater concentration, and in that:

- said measuring chamber (11) is directly connected to the mixing chamber (14) to allow an immediate, or nearly immediate transfer, of at least part of the biological sample mixed from the mixing chamber (14) to the measuring chamber (11) at the start of the reaction of the reactive agent with the components of the biological sample, and to perform, by means of said measuring means of the photometric type (13), a measurement of the initial concentration of the components and/or reactive agents in said biological sample, said measuring being carried out simultaneously and dynamically with respect to the progress of the reaction in the mixing chamber (14), said measuring being carried out by evaluating, by means of said processing and control means (40), the slope of the line (r, t) tangent to the initial point of the reaction kinetics of the biological sample, and comparing the initial reaction speed of the biological sample, represented by the slope of said line (r, t) and the initial reaction speed of the standard reactive agent with greater concentration, represented by the slope of said line (s), so as to detect in advance, before the end of said reaction in the mixing chamber (14), a possible prozone effect in the biological sample analyzed.

10. Apparatus as in claim 9, characterized in that it comprises dispensing means (17) able to deliver said reactive agent and/or said biological sample into the mixing chamber (14) in micro-voluminal quantities, in order to modify in a controlled manner the concentration of said biological sample.

11. Apparatus as in claim 10, characterized in that said electronic processing and control means (40) are associated both with the measuring means (13) and also with the dispensing means (17), and are able to control the dispensing means (17) for the controlled delivery of the reactive agent and/or the biological sample into the mixing chamber (14) according to the measurements made by the measuring means (13).