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Measuring range extension of chromatographic rapid testsRelated Patent Categories: Chemistry: Molecular Biology And Microbiology, Measuring Or Testing Process Involving Enzymes Or Micro-organisms; Composition Or Test Strip Therefore; Processes Of Forming Such Composition Or Test Strip, Involving Virus Or BacteriophageMeasuring range extension of chromatographic rapid tests description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080070234, Measuring range extension of chromatographic rapid tests. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] The present invention relates generally to methods and devices for the quantitative determination of an analyte in a sample and, in particular, to methods for extending the quantitative measuring range of an analyte in a sample, and test devices employing same. [0002] A widespread analytical method for the rapid determination of analytes such as, for example, drugs, pregnancy hormones; infectious diseases or cardiac markers utilizes immunological test strips. In this connection qualitative tests that are read purely visually (e.g., Roche CARDIAC.RTM. D-dimer, Trop T sensitive, etc.) as well as quantitative tests that are evaluated by means of a reading device (e.g., Elecsys.RTM. proBNP, Roche CARDIAC.RTM. proBNP, etc.) are widely used. [0003] Such quantitative immunological test strips are characterized in particular by their easy handling. The test strips are usually based on the fact that the test strip contains a reagent which leads to a detectable signal by reaction with the analyte in the sample. The detectable signal is usually determined by reflectance measurement after a specified time period. The time period between contacting the analyte and reagent and measuring the signal is chosen to be as long as possible. This ensures a long reaction time between the reagent and analyte and thus ensures the highest possible sensitivity of such test strips. However, for reasons of reaction kinetics it is no longer possible after such a long reaction period to quantitatively determine analytes which are present in a high concentration in a sample. [0004] Hence, such test strips still have considerable weaknesses with regard to their performance compared to conventional laboratory analytical systems such as, e.g., Elecsys.RTM. (Roche Diagnostics), IM (Abbott), Dimension.COPYRGT. (Dade Behring). Especially the measuring accuracy and the dynamic measuring range are considerably impaired in test strips for example in comparison to reactions in solution. This limits their use when determining analytes which require a high sensitivity as well as the measuring range as large as possible. In particular, for the emergency care of patients it would be very helpful for the attending physician if a test or a method could be provided which, due to its high sensitivity, could, on the one hand, enable certain diseases to be reliably excluded but, on the other hand, would also provide a large measuring range. A large measuring range for an analyte is particularly desirable for risk stratification and for therapeutic monitoring. A measuring range extension of tests would be particularly desirable for those pathological conditions in which the concentration of an analyte or marker that is characteristic for the condition correlates with the severity of the pathological condition. An elevated marker concentration (e.g., NT-proBNP) can in such cases indicate an increased risk situation for a patient. SUMMARY OF THE INVENTION [0005] It is against the above background that the present invention provides certain unobvious advantages and advancements over the prior art. In particular, the inventors have recognized a need for improvements in methods for extending the quantitative measuring range of an analyte in a sample. [0006] Although the present invention is not limited to specific advantages or functionality, it is noted that the methods according to the invention enable the upper limit of the measuring range to be increased by more than three-fold compared to the known methods of the prior art. The methods according to the invention thus improve the diagnostic competence of the attending physician. [0007] The extended measuring range of a test according to the invention may also enable additional, often laborious tests (e.g., invasive diagnostic methods, etc.) to be dispensed with. [0008] As described in detail below, the methods according to the invention enable a more rapid determination of concentrations than methods or tests that have been described in the prior art especially with high analyte concentrations in a sample. Since, for example, the blood levels of NT-proBNP correlate with the degree of cardiac dysfunction, the methods according to the invention allow a more rapid assessment of the cardiospecific status of a patient in emergency situations. This gives rise to the advantage that when acute cardiac events occur such as for example an acute myocardial infarction, patients can be identified and adequately treated at an earlier time than is the case with the current diagnostic procedures. The methods according to the invention and the ability to make a more rapid diagnosis especially in the case of an acute cardiac event, enable the attending physician to more rapidly initiate appropriate countermeasures and can thus reduce other cardiac complications and the mortality rate. [0009] In accordance with one embodiment of the present invention, a method for the quantitative determination of an analyte in a sample is provided comprising: [0010] (a) providing an analyte-specific substance which is able to undergo a reaction which generates a detectable signal when it is contacted with an analyte, [0011] (b) providing at least two calibration graphs which have been generated by reacting in each case the same analyte-specific substance with different amounts of in each case the same test analyte for in each case a predetermined reaction time, [0012] (c) contacting the analyte-specific substance with a sample which contains the analyte to be detected, [0013] (d) measuring the signal at a first predetermined reaction time for which a first calibration graph according to (b) is provided, [0014] (e) checking whether the signal measured according to (d) enables a quantitative determination of the analyte with a desired accuracy, [0015] (f) (i) quantitatively determining the analyte on the basis of the signal measured according to (d) if the desired accuracy is reached, [0016] or [0017] (ii) measuring the signal at a second predetermined reaction time for which a second calibration graph according to (b) is provided, [0018] (g) checking whether the signal measured according to (f)(ii) enables a quantitative determination of the analyte with a desired accuracy, and [0019] (h) (i) quantitatively determining the analyte on the basis of the signal measured according to (f)(ii) if the desired accuracy is reached, [0020] or [0021] (ii) continuing the determination at at least one further predetermined reaction time (corresponding to (f)(ii), (g), (h)(i)). [0022] The method can further comprise: [0023] (i) measuring the signal at a third predetermined reaction time for which a third calibration graph according to (b) is provided, [0024] (j) checking whether the signal measured according to (i) enables a quantitative determination of the analyte with a desired accuracy, and [0025] (k) (i) quantitatively determining the analyte on the basis of the signal measured according to (i) if the desired accuracy is reached, [0026] or [0027] (ii) continuing the determination at at least one further predetermined reaction time. [0028] The steps (f)(ii), (g) and (h)(i) of the method can be repeated as often as desired. In a typical embodiment these steps are repeated two or three times, i.e., two or three calibration graphs for two or three predetermined reaction times are generated or provided. [0029] In accordance with yet another embodiment of the present invention, a method for the quantitative determination of an analyte in a sample is provided comprising: [0030] (a) providing an analyte-specific substance which is able to undergo a reaction which generates a detectable signal when it is contacted with an analyte, [0031] (b) providing at least two calibration graphs which have been generated by reacting in each case the same analyte-specific substance with different amounts of in each case the same test analyte for in each case a predetermined reaction time, [0032] (c) contacting the analyte-specific substance with a sample which contains the analyte to be detected, [0033] (d) measuring a first signal at a first predetermined reaction time for which a first calibration graph according to (b) is provided, [0034] (e) measuring a second signal at a second predetermined reaction time for which a second calibration graph according to (b) is provided, [0035] (f) optionally measuring a further signal, [0036] (g) checking which of the signals measured according to (d), (e) or (f) enables a sufficient accuracy for the quantitative determination of the analyte, and [0037] (h) quantitatively determining the analyte on the basis of the signal which enables an adequate accuracy. [0038] In order to check whether the first measured signal or the second measured signal enables the analyte to be quantitatively determined with a greater accuracy, an empirical concentration limit is defined in a typical embodiment on the basis of the at least two calibration graphs that are provided. Analyte concentrations which exceed this limit are evaluated according to the shorter of the two reaction times whereas analyte concentrations which fall below this limit are determined according to the longer of the two reaction times. If it is found that the analyte concentration exceeds the limit after the short reaction time, i.e., a high analyte concentration is determined, the method can be stopped at this time. [0039] These and other features and advantages of the present invention will be more fully understood from the following detailed description of the invention taken together with the accompanying claims. It is noted that the scope of the claims is defined by the recitations therein and not by the specific discussion of features and advantages set forth in the present description. BRIEF DESCRIPTION OF THE DRAWINGS [0040] The following detailed description of the embodiments of the present invention can be best understood and is elucidated in more detail when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which: [0041] FIG. 1 shows the reflectance kinetics of CARDIAC.RTM. proBNP after 6 min, 8 min and 12 min. The reflectance [%] is plotted against the concentration of proBNP [pg/ml] which was determined by the Elecsys.RTM. proBNP reference test. [0042] FIG. 2 shows a comparison between the method according to an embodiment of the present invention using a CARDIAC.RTM. proBNP test strip and the Elecsys.RTM. proBNP test. DETAILED DESCRIPTION OF THE INVENTION [0043] In accordance with a typical embodiment of the present invention, a liquid sample typically derived from body fluid is used. A blood, plasma, serum, saliva or urine sample is more typically used. [0044] The analyte to be determined quantitatively is typically selected from nucleic acids, lipids, carbohydrates, proteins and in particular from DNA, RNA, antibodies, antigens, metabolic products, hormones, viruses, microorganisms, cells, cardio-specific markers, neurohormonal markers, ischaemic markers and muscle-specific markers. [0045] Typical examples of lipids include cholesterol, HDL cholesterol and triglycerides. A typical carbohydrate analyte is glucose. Examples of enzymes to be determined include alkaline phosphatase and amylase. Uric acid, bilirubin and urobilinogen are examples of typical metabolic products. Continue reading about Measuring range extension of chromatographic rapid tests... 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