Circulating calcium is normally controlled within very narrow limits. This patient's results indicate marked hypercalcemia combined with depressed phosphate. The chloride-to-phosphate ratio can be a rough guide to whether a decrease in phosphate is specific for phosphate, or affects all negative ions. In this case, the elevation in the CL:PO4 ratio indicates that phosphate is specifically decreased.
The differential diagnosis of hypercalcemia includes hyperparathyroidism, drug-induced effects, hypercalcemia of malignancy, sarcoidosis, multiple myeloma, and other less common conditions. The combination of elevated calcium and decreased phosphate is most commonly associated with hyperparathyroidism.