The chloride phosphate ratio as the screening test for primary hyperparathyroidism.

Serum chloride and phosphate concentrations were measured in 79 hypercalcemic patients. The chloride values were higher (mean 106.7 mEq/l) and phosphate lower (mean 2.08 mg/100 ml) in the 53 hyperparathyroid patients, where as the chloride concentrations were lower (mean 99.3 mEq/l) and phosphate higher (mean 4.07 mg/100 ml) in the 26 patients with hypercalcemia from other causes. The chloride phosphate ratio ranged from 19 to 32 in the subjects with hypercalcemia from other causes with 90 per cent of values less than 30. In patients with primary hyperparathyroidism we found 96 per cent of the values more than 34. From our experience with chloride phosphate ratio it seems to us that this ratio is a very useful and simple preliminary test for distinguishing patients with primary hyperparathyroidism from patients with hypercalcemia from other causes, with normal renal functions.