Sensitive time-resolved fluoroimmunoassay of salmon calcitonin

A two-site assay was developed by use of the "dissociation and enhancement lanthanide fluoroimmunoassay" (DELFIA) technique for determination of salmon calcitonin (SCT) in serum after administration to osteoporotic patients. Polyclonal antibodies were produced in rabbits immunized with SCT coupled to ovalbumin. After affinity purification, the antibodies were used both as immobilized capture antibodies and as Eu-chelate-labeled signal antibodies. A sensitive assay with a detection limit of 1.1 pmol/L was achieved, and no cross-reaction with human calcitonin was observed. The intra- and interassay CVs were < 12% (n = 10) and < 15% (n = 4), respectively. Analytical recovery of SCT added to serum was 91% +/- 3% (mean +/- SD, n = 4). SCT was measurable in all the samples from eight osteoporotic patients after subcutaneous SCT administration. We conclude that this new sensitive and specific two-site DELFIA can reliably measure SCT in serum.