Calcitonin levels in normal individuals with new highly sensitive chemiluminescent enzyme immunoassay.

Human serum calcitonin concentration in normal individuals was measured with a new assay based on the chemiluminescent enzyme immunoassay (CLEIA) method. The CLEIA assay was highly sensitive and was able to determine a calcitonin concentration of 0.04 pg/ml as sensitivity limit at a condition of 0+3SD. With this CLEIA assay, the mean value of calcitonin in males and females was 2.26 and 1.33 pg/ml, respectively, highlighting a significant difference between genders. The mean value and range of human serum calcitonin in this assay were approximately 1/10 those reported previously in competitive radioimmunoassay (RIA) methods. Since RIAs for calcitonin showed much variability at a low concentration range due to the competitive format, they seemed to lack the necessary sensitivity to cover the normal range and appeared only useful for hyper-calcitonin phenomenon in diseases such as medullary thyroid carcinoma. The CLEIA for calcitonin provided a lower detection limit than normal range, and it can therefore be assumed that it could be applied for the measurement of hypo-calcitonin phenomena typically found in some disorders such as osteoporosis.