[Erythrocytosis and hydronephrosis in a horseshoe kidney].
OBJECTIVE: To report a case of erythrocytosis in a patient with a hydronephrotic horseshoe kidney and normal erythropoietin values. METHODS/RESULTS: A hydronephrotic horseshoe kidney was discovered during evaluation to determine the etiology of the erythrocytosis in a 23-year-old male with normal erythropietin values. Blood parameters returned to normal following heminephrectomy. The hydronephrosis had been caused by stenois of the pyeloureteric junction. CONCLUSIONS: Although erythropoietin values may be normal, hydronephrosis can cause secondary erythrocytosis.