This patient presents with recurrent gross hematuria. The absence of active urinary sediment makes intrinsic glomerular disease less likely. The normal ultrasound findings and lack of clinical symptoms also makes a structural kidney lesion, kidney stone, or urinary tract infection less likely. Since he is a young African American, there is a high probability of sickle cell trait causing his gross hematuria, and the diagnosis can be confirmed with hemoglobin electrophoresis.
Hematuria and impaired ability to maximally concentrate the urine are two renal abnormalities encountered in patients with sickle cell trait. The renal papilla is a hypoxic and hypertonic environment, and papillary blood velocity is relatively slow - all conditions which favor sickling of cells. This results in renal papillary infarction and possible papillary necrosis.
This patient has no symptoms of a systemic autoimmune disorder, red blood cell casts, or significant proteinuria on urinalysis to suggest the possibility of an autoimmune disorder and associated glomerulonephritis.