Maximizing the value of laboratory tests

Sources of error in laboratory tests include preanalytical, analytical, and postanalytical factors that potentially influence the integrity or interpretation of a test result. Immunoassays that are used to measure many of the endocrine biomarkers such as hormones, binding proteins, and metabolic products, are particularly susceptible to analytical interferences due to the limited specificity of antibody-antigen interactions. Endogenous substances such as lipids and bilirubin may interfere with laboratory tests when present at unusually high concentrations. Hemoglobin is a common interferent that leaks into the noncellular fraction of blood when red blood cells are disrupted during collection or storage of a blood specimen. Dietary supplements such as biotin can sometimes interfere with laboratory tests when present at high enough concentrations. Finally, the proper interpretation of a laboratory test result requires some knowledge of the sensitivity and specificity of the test, the predictive value of positive results, and the inherent biological variability of the biomarker the test measures. This chapter discusses the most common sources of error in laboratory tests used in diagnostic endocrinology. Avoidance of these sources of error maximizes the value of laboratory tests.