Lithium has been reported to raise serum calcium and lower serum
phosphate concentrations and to increase urinary calcium excretion. Because
these changes may be effects of parathyroid hormone (PTH), PTH was measured
in 19 patients receiving lithium. PTH was significantly higher in these
patients than in 150 normal subjects. For all patients serum calcium
concentrations correlated significantly with serum lithium concentrations.
These results indicate that lithium may cause biochemical
hyperparathyroidism. Secondary hyperparathyroidism in certain patients with
lithium nephrotoxicity is also possible.