Ringel, Matthew D

Abstract BACKGROUND The objective of this study is the validation and proof of clinical relevance of a novel electrochemiluminescence immunoassay (ECLIA) for the determination of serum calcitonin (CT) in patients with medullary thyroid carcinoma (MTC) and in different diseases of the thyroid and of calcium homeostasis. METHODS This was a multicenter prospective study on basal serum CT concentrations performed in 9 US and European referral institutions. In addition, stimulated CT concentrations were measured in 50 healthy volunteers after intravenous calcium administration (2.5 mg/kg bodyweight). RESULTS In total, 1929 patients and healthy controls were included. Limits of blank, detection, and quantification for the ECLIA were 0.3, 0.5, and 1 ng/L, respectively. Highest intra- and interassay coefficients of variation were 7.4% (CT concentration, 0.8 ng/L) and 7.0% (1.1 ng/L), respectively. Medians (interval) of serum CT concentrations in 783 healthy controls were 0.8 ng/L (<0.5–12.7) and 3 ng/L (<0.5–18) for females and males, respectively (97.5th percentile, 6.8 and 11.6 ng/L, respectively). Diagnostic sensitivity and specificity were 100%/97.1% and 96.2%/96.4%, for female/males, respectively. Patients (male/female) with primary hyperparathyroidism, renal failure, and neuroendocrine tumors showed CT concentrations >97.5th percentile in 33%/4.7%, 18.5%/10%, and 8.3%/12%, females/males, respectively. Peak serum CT concentrations were reached 2 min after calcium administration (161.7 and 111.8 ng/L in males and females, respectively; P < 0.001). CONCLUSIONS Excellent analytical performance, low interindividual variability, and low impact of confounders for increased CT concentrations in non-MTC patients indicate that the investigated assay has appropriate clinical utility. Calcium-stimulated CT results suggest good test applicability owing to low interindividual variability.