Serum Levels of Coll2-1, a Specific Biomarker of Cartilage Degradation, Are Not Affected by Sampling Conditions, Circadian Rhythm, and Seasonality.

Objective: To assess intraindividual biological variability of serum cartilage specific biomarker Coll2-1 and define the best standardized conditions for blood sampling.

Design: Blood samples were taken from 116 subjects with knee osteoarthritis (OA) at a single time point (PRODIGE study) and from 15 healthy subjects under various conditions, including fasting condition, sampling time and season, blood treatment, and type of blood collection tube (COVAR study). Type II collagen-specific biomarker Coll2-1 was directly measured in serum using an immunoassay.