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All the tests in clinical laboratories are susceptible to preanalytical variables that can affect test results before a specimen is even analyzed. These variables include physiologic or nonphysiologic in nature and include types of collection devices, stature of patient during the collection, diet, circadian rhythms, the environment where the specimen is collected, proper blood collection techniques, the effect of drugs that the individual takes, and others. In addition to preanalytical variables, there are analytical and postanalytical factors that can cause erroneous test results. Traditionally, immunoassays (IAs) have been the most commonly used laboratory analyses for endocrine evaluation. Like all laboratory tests, they are affected by the factors described above; however, because of the numerous configurations of IA, these effects occur in varying degrees and directions. Several methods and techniques have been developed to mitigate the interferences, which has led to the rise of liquid chromatography with tandem mass spectrometry as the state-of-the-art method for measuring hormones and other molecules found in very low concentrations in human specimens. Both clinical biochemists and clinicians should be familiar with these factors and consider them whenever a test result does not match the clinical picture. In addition the clinician who interprets the test result must be aware of each test’s reliability for both ruling in or ruling out the disease in question. Application of the test result to the detailed clinical assessment will permit the best overall use of the laboratory in medicine. This chapter describes all the above factors in details. |
