Biological and analytical variation of clinical biomarker testing: implications for biomarker-guided therapy.

Testing for serum-based biomarkers are essential for diagnosis, risk stratification, and management of patients with cardiovascular disease. All biomarker assays have inherent analytical variability (coefficient of variance CVA), ranging from 5-20 %. There are also variances within a subject over time (CVI) and between subjects (CVG). Variances are determined by experimentation under controlled conditions on healthy subjects. Once measured, the index of individuality (II), reference change value (RCV), and number of samples to establish a homeostatic set point can be calculated. These attributes affect how results of biomarker tests are interpreted in routine clinical practice such as cardiac troponin for acute coronary syndromes, the natriuretic peptides, galectin-3 and sST2 for heart failure, lipids and lipoproteins for primary cardiovascular disease risk, and liver function tests and skeletal muscle biomarkers for detecting complications from statin use.