Hyperscalcemia of Thyrotoxicosis

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Abstract
Records of 302 patients with hyperthyroidism were reviewed for evidence or manifestations of hypercalcemia. Serum Ca was measured by a modified Clark-Collip method in 46 of 203 hyperthyroid patients (Group I) and by atomic absorption spectrophotometry in 31 of 59 hyperthyroid patients (Group H). Determinations were compared to normal values. The proportion of elevated serum Ca determinations in Groups I and n (greater than 10.9 and 10.6 mg/100 ml respectively) was 23.0% (14 determinations in 12 patients) and 15.6% (7 determinations in 5 patients) respectively. This incidence of hypercalcemia was highly significant when compared to the incidence In apparently normal individuals (P < 0.005 and P < 0.001 respectively) or In consecutive determinations on hospital patients with various disorders (P < 0.001 and P < 0.005 respectively). The Ca elevations ranged as high as 12.4 mg/100 ml, but diffusible Ca levels were possibly greater than the total serum Ca indicated since most patients had low serum albumin levels. Hypercalcemia appeared to be related to the hyperthyroid state since it was not seen when the patients became euthyrold, but could not be significantly correlated with elevations of the protein bound iodine or with symptomatology. Hyperthyroidism is only rarely associated with renal damage that might be attributed to hypercalcemia. Two of the hyper- thyroid patients also had parathyroid tumors; however, in one of these the tumor was found only after the onset of renal failure.

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