Pseudohypercalcaemia in two patients with IgM paraproteinaemia

A 63-year-old man presented in 1992 with left basal pneumonia and septicaemia. Protein electrophoresis revealed a dense discrete and abnormal band in the gamma region. His serum IgM concentration was grossly increased at 82·8 giL (reference range 0,42-2'6) and bone marrow biopsy revealed an increase in lymphoid cells, some of which showed plasma cell characteristics of binucleate forms consistent with Waldenstrom's macroglobulinaemia. He was treated with intermittent courses of chlorambucil and prednisolone with a satisfactory response, and his IgM fell to 20 g/L. His serum calcium adjusted for albumin was normal at 2·53 rnmol/L on presentation, but increased to 2·84mmol/L in August 1993 and then to 3·55 mrnol/L in December 1994 (Fig. 1). His serum parathormone (PTH) concentrations measured on three occasions when he was hypercalcaemic were within the reference range (Chi ron Magic LitePTH =2-4, 2·5 and 2·5 pmol/L; reference range 0'9-5-4) but were inappropriate for his degree of hypercalcaemia. He had normal thyroid function, and no evidence of sarcoidosis. His parathormone related peptide was below the limit of detection and his urinary calcium excretion was normal at 5·0 mmol/24 h. Radiological examination revealed osteoporosis of his