Reference range and short- and long-term biological variation of interleukin (IL)-6, IL-17A and tissue necrosis factor-alpha using high sensitivity assays.

Interleukin (IL)-6, and tissue necrosis factor alpha (TNF-α) are established biomarkers for clinical practice and use in clinical trials of patients with cardiovascular disease. IL-17A may be an emerging marker for atherosclerosis disease progression. We measured IL-6, TNF-α, and IL-17A using a high sensitivity immunoassay (Erenna, Singulex, Inc.) to determine the reference range and to calculate the weekly (25 subjects over 6weeks) and monthly (17 subjects over 9months) biological variation (BV) from apparently healthy subjects and those attending a cardiovascular disease clinic. As a validation for the experimental and statistical approach taken, the weekly BV for high sensitivity C-reactive protein was also determined and result compared to previous reports. The upper 95th percentile reference limit for IL-6, TNF-α, and IL17-A was 4.45, 2.53, and 1.93pg/mL, respectively. The intra-individual variability ranged from 21% to 57% and the inter-individual variation ranged from 22% to 53%. The corresponding index of individuality was 0.65-1.6 and reference change values from 63% to 161%. The BV for IL-6 and TNF-α are similar to previous reports, documenting their diagnostic utility in clinical practice. Up until now, the biological variation of IL-17A and upper reference limit has not been previously reported, thereby limiting the use of this marker in clinical trials.