Protein correction of serum calcium in mild primary hyperparathyroidism.
Simultaneous determinations of serum total calcium(TOCa), protein corrected total calcium (TOCac), ultrafiltrable calcium (UFCa) and ionised calcium (Ca++) were undertaken in 63 controls and in 76 patients with primary hyperparathyroidism. Raised levels of Ca++ were used as one criterion of the diagnosis which was confirmed by operation in all. For the purpose of estimating the relative value of TOCa and TOCac in the detection of mild hyperparathyroidism we selected all patients with TOCa values below 3.00 mmol/l (n = 46). As a group these patients turned out to be mildly hypoproteinaemic (p less than 0.01), probably because of high age and complicating conditions. Further subdivision of this group into frank hypercalcaemia, borderline hypercalcaemia and normocalcaemia was undertaken according to the respective 99% and 95% confidence limits of normal. Twenty-seven patients were classified as frankly hypercalcaemic by TOCa as well as by TOCac. The distribution of the remaining 19 patients within the three categories was 1:6:12 as judged from TOCa while TOCac gave a better distinction from normal, 9:4:6 (p less than 0.01). This compared well with the classification obtained by UFCa, 10:5:4. It is concluded that TOCac is definitely advantageous to TOCa in the detection of hypercalcaemia in mild primary hyperparathyroidism.