A 12-YEAR-OLD otherwise healthy boy was examined owing to a 3-month history of recurrent gross hematuria. This disorder occurred after exercise and vanished within 6 hours. The child denied weight loss, anorexia, nausea, vomiting, constipation, abdominal or flank pain, dysuria, polyuria, polydipsia, fever, or muscle weakness. He had no history of urinary tract infection or chronic renal disease. He was receiving no medications except acetaminophen for occasional headaches. The family history was remarkable for kidney stones in a maternal uncle.
The physical examination showed a well-appearing boy of white and Filipino ancestry. Height and weight were at the 10th and fifth percentiles, respectively, for age. Serial blood pressure measurements were within normal limits for his age. There were no neck masses, and the remainder of the physical examination was normal.
A urinalysis was negative for protein but showed microscopic hematuria with 100 red blood cells per high-power field. Two urine