Diurnal Patterns of Serum Immunoreactive Calcitonin in Healthy Males and in Insulin Dependent Diabetics

SUMMARY Serum immunoreactive calcitonin (iCT) was measured half‐hourly for 27 h in five healthy males and four insulin dependent juvenile diabetic males during normal activity. In another group of four healthy males studied during 12 h the first meal was postponed 8 h. Duplicate measurements of an internal reference standard in all radioimmunoassay runs gave a mean value of 58 pg/ml with an intra‐assay variation of 4.7 pg/ml (SD) and an interassay variation of 10.8 pg/ml (SD). Results of serum iCT determinations in one subject were excluded as the majority of values were below the lower limit of detection (20 pg/ml). For all three groups serum iCT levels varied little and unsystematically during day and night‐time and no diurnal peaks were observed. Food intake did not affect serum iCT levels significantly. With the present radioimmunoassay, results of serum iCT measurements can thus be interpreted without taking the sampling time or meals into account. Expert technical assistance has been provided by Inga Bisgaard, Joan Hansen, Janet Mikkelsen, and Birgit Mortensen. This work was supported by grants from the Danish Cancer Society, the Danish Medical Research Council, and the Institute of Experimental Clinical Research, University of Aarhus.