Specificity of Detection
The detection of a particular analyte in a biological sample is highly influenced by several experimental factors. These factors include the physical treatment of the sample (e. g., filtering or centrifugation,) the chemical treatment of the sample (e. g., the use of reagents to derivatize the analyte of interest or to adjust the pH,) the measurement conditions (e. g., incubation temperature) as well as the nature of analytical signal itself (e. g., spectral or potentiometric.) When all the experimental and measurements factors are considered, a detection scheme can be specific (the analytical signal is attributed to the analyte of interest only) or non-specific (the analytical signal is attributed to the analyte of interest and other possible analytes in the sample.) In between these two extremes there is a wide spectrum of selectivity. The higher the selectivity, the larger the portion of the analytical signal that can be attributed to the analyte of interest.
The specificity of detection is critical because biological samples, such as blood, are very complex mixtures of many chemicals. In addition to the analyte of interest, biological samples contain chemicals that are produced naturally by the human body and metabolites of drugs taken by patients in hospitals and at home. The nature and the amounts of the naturally produced analytes may change as the medical condition of a patient changes. This complex sample environment (known also as the sample matrix) makes it necessary to test the performance of any quantitative medical device under a large number of chemical conditions. In order to ensure patient safety, it is important to study the effects of these naturally occurring chemicals and drug metabolites on the accuracy of quantitative medical devices. This is known as testing the interference effects. Because such testing is both costly and time-consuming, it is extremely desirable that the detection of the analyte(s) of interest is either specific or highly selective. Examples of such preferred detection schemes include the use of antibodies and nucleic acid probes as well as immobilized enzymes.