Standardization and clinical application of a radioimmunoassay for human calcitonin

A radioimmunoassay for the measurement of Human Calcitonin (HCT) is described. Serum levels of HCT in normal subjects and in individuals under different pathological conditions have been studied with this method. HCT labelling is performed following the chloramine T method of Hunter and Greenwood. Adding successively Quso G-32 (a finely powdered silica) and an anion exchange resin (AGI-X10 resin), to the tracer, reduces both the damaged fraction and the free isotope which originate during storage. Purification of the labelled hormone is carried out through a Sephadex G-50 gel column. Sera stored at --20 degrees C preserves its immunoreactivity up to 4 months after extraction. The mean basal HCT levels in 110 fasting normal persons is 277 +/- 123 pg/ml (undetectable 8.28%). No significant correlation between HCT levels and various serum ions has been observed. Basal HCT values in seven patients with medullary thyroid carcinoma (MTC), oscillated between 5 and 110 ng/ml, while in six other patients with non medullary thyroid carcinoma the values remained within normal range. Both a calcium infustion and a pentagastrin injection are used to stimulate HCT secretion. The increase of HCT basal levels produced by the latter in normal controls and in patients with MTC, is faster and more intense. Calcium infusion produced a significant correlation between calcium and the increased HCT levels only in patients affected with MTC.