Nephrocalcinosis: another cause of renal erythrocytosis.

Nephrocalcinosis: another cause of renal erythrocytosis Although erythrocytosis is not a recognised complication of nephro-calcinosis, in the course of a study of 250 patients with nephro-calcinosis we found nine patients with raised blood haemoglobin concentration and haematocrit value. All patients had radiological medullary nephrocalcinosis, of varying underlying cause (two primary hyperparathyroidism, three renal tubular acidosis, four medullary sponge kidney). Studies of red cell mass and plasma volume were performed on six patients using 51Cr-labelled autologous red cells.' Urine erythropoietin concentration was measured in four of these patients, and in 11 other patients with nephrocalcinosis but no erythrocytosis: the commercially prepared JCL-ECF haemagglutination-inhibition assay for erythroid stimulating factors (JCL Clinical Research Co, Knoxville) was used for this assay. Urine was studied fresh or was immediately deep frozen until the assay could be performed. All patients had polyuria and a urine concentration defect, an almost invariable feature of nephrocalcinosis,2 So any rise of urine erythropoietin concentration probably represented a true increase in erythropoietin excretion. The results are shown in the table. Five of the six patients studied had a decreased plasma volume. Four of six patients studied had a definitely raised red cell mass, and one a marginally raised red cell mass. One other patient had significantly increased red cell production despite a blood haemoglobin concentration of 18 2 g/dl and haematocrit value of 57 %'. Thus, of seven patients studied, five had true erythrocytosis, one marginal erythrocytosis, and one pseudoerythrocytosis. In the three patients studied whole blood viscosity was above the upper limit of normal. Platelet and white cell counts were normal in all patients. Urine erythropoietin concentration was raised in three of the four patients studied with erythrocytosis, and the normal value in patient 9 may be inappropriately high for someone with a haemoglobin concentration of 18 2 g/dl. Urinary erythropoietin concentration measured in 11 other patients with nephrocalcinosis (four with renal tubular acidosis, seven with medullary sponge kidney) was considerably raised in five, mildly raised in four, and normal in two. Comment Erythropoietin is a glycoprotein of molecular weight 36 000,3 and, like small-molecular-weight proteins, is probably filtered by the renal glomerulus and reabsorbed by the proximal tubule. The increased urinary erythropoietin in these patients is unlikely to have been due to tubular damage, as they have no evidence of abnormal tubular handling of amino-acids, glucose, or '5,-microglobulin. Thus the increased erythropoietin excretion of these patients is probably secondary …