A survey of diagnoses in patients with a low intact parathyroid hormone concentration.

Intact parathyroid hormone (PTH) was analysed in 1107 samples over a 13 month period. Of these, 181 samples (16%) gave results of < or = 1 pmol/L and the case notes of 169 of these 181 patients were examined. Eighty-two patients (48%) were hypercalcaemic at the time of the PTH assay. As expected, the most common diagnosis in this group was hypercalcaemia of malignancy but surprisingly this accounted for only 42 of the hypercalcaemic patients; an unexpectedly high proportion (20 patients) had chronic renal failure with hypercalcaemia due to excessive treatment with 1 alpha-hydroxycholecalciferol; eight patients had transient unexplained hypercalcemia and the remaining 12 patients were hypercalcaemic for a variety of causes including immobilization, bendrofluazide treatment and Paget's disease. Fifty-nine patients (35%) were normocalcaemic: 26 had osteoporosis, 10 had chronic renal failure and the remainder had a wide range of diagnoses. It is possible that the low intact PTH result in a proportion of the normocalcaemic group was caused by ingestion of calcium tablets prior to blood sampling for PTH. Twenty-eight patients (17%) were hypocalcaemic: 24 of these had hypoparathyroidism, two had chronic renal failure and two had transient unexplained hypocalcaemia.