Biological variation and reference change values: an essential piece of the puzzle of laboratory testing

摘要

The biological variability of analytes assessed in clinical laboratories is pivotal to understand several issues related to the quality of laboratory information throughout all steps of the testing process (Figure 1). In the pre-analytical phase, the knowledge of predictable biological cyclical biorhythms is required for appropriate collection of specimens at times pertinent to the clinical questions. Daily, monthly and seasonal rhythms have been broadly described and all play a critical role for addressing proper sample collection but also for interpreting test results (1, 2). This is the typical case of serum cortisol in Cushing's disease, as it is widely recognized that the 24 h cortisol secretory pattern is characterized by a lack of normal circadian variation (3).