Reference range of serum calcitonin levels in humans: influence of calcitonin assays, sex, age, and cigarette smoking

Objective: The objective of this study was to re-evaluate the adult C-T reference values determined by five different immunoassays and by introducing criteria for selecting control subjects. Design: A prospective multicenter study. Patients: Three hundred and seventy-five clinically euthyroid subjects. Methods: We used five different C-T immunoassays. Sera were assayed for the concentration of TSH, gastrin, procalcitonin, urea, calcium, and anti-thyroperoxidase antibodies. Results: Screening for the various potential causes of hypercalcitoninemia led to the exclusion of 23%, of the sera. Our reference value analysis dealt with 287 subjects (142 men and 145 women). The proportion of samples in which no C-T was detected varied from 56% (for assay D) to 88% (for assay C). We observed significant correlations (whose magnitude depended on the assay used) between G,. levels and age or body mass index (BMI) (primarily in men). The distribution of C-T. levels showed that 4.7, 9.8, 2.5, 6.5, and 8.0% of the values were over 10 pg/ml respectively. These values corresponded essentially to samples from 11 male subjects (median age: 55 years), most of whom were smokers. The highest C-T. values were around twice as high in men than women, and were higher in smokers than non-smokers. Conclusion: In clinical practice (and after having excluded the usual causes of raised C-T levels), the interpretation of C-T assay results must take into account i) the method used; ii) the patient's gender, age, and weight; and iii) the potential influence of cigarette smoking.