Hyperphosphatemia in multiple myeloma.

We report three cases of IgG kappa multiple myeloma with pseudohyperphosphatemia. The patients' serum calcium levels were normal, and the hyperphosphatemia was not related to impaired renal function. No hypoparathyroidism was found, and no exogenous phosphate preparation had been given. Since the hyperphosphatemia was of no obvious clinical or physiological significance, as evidenced by normal serum levels of 1,25 dihydroxy vitamin D3, it was diagnosed as spurious and was connected to interference of the paraprotein with the chromogenic assay. In two of the patients major fluctuations in serum phosphate levels were seen, induced by the changes in globulin and paraprotein levels that occurred during therapy and relapse.