[Induced hypocalcaemia test using salmon calcitonin as a means for the evaluation of osteoclastic activity (author's...

The authors measured the degree of hypocalcaemia (delta Ca S), hypophosphataemia and the fall in urinary hydroxyproline excretion induced by an intramuscular injection of 100 MRC U of synthetic salmon calcitonin (S.C.T.) during the 24 hours following the injection. In 15 control subjects, the fall in plasma calcium was slight ( - 2.1 +/- 0.9 mg/l) but significant. In bone diseases involving hyperosteoclastosis, the degree of hypocalcaemia was much greater: 10.6 +/- 1.1 mg/l in 24 cases of Paget's disease, - 9.0 +/- 1.6 mg/l in 5 cases of diffuse malignant disease of bone, - 8.0 +/- 1.4 mg/l in 6 cases of primary hyperparathyroidism and - 3.5 +/- 0.8 mg/l in 13 cases of algodystrophy of the limbs. In the subjects studied as a whole there was a significant linear relationship between the delta Ca S and the extent of the trabecular surfaces of osteoclastic resorption, but not between delta Ca S and total 24 hour urinary hydroxyproline excretion. The S.C.T. hypocalcaemia test would appear to be a simple means for the evaluation of osteoclastic activity within the skeleton, and thus to select those bone disorders which should respond to antiosteoclastic therapy (calcitonin, diphosphonates).