When hematuria is of renal glomerular or tubular/interstitial origin, a relatively small amount of blood is diluted by tubular fluid and urine. Also, tissue plasminogen and urokinase are present within the tubules and glomeruli. Consequently, glomerular and other intrarenal causes of hematuria are rarely, if ever, associated with the passage of clots into the urine.
This patient has a history of cyclophosphamide exposure and presents with painless hematuria in the absence of urinary tract symptoms. Evaluation for bladder lesions via cystoscopy would have the highest diagnostic yield. Cyclophosphamide can induce a chemical cystitis and be associated with the development of bladder cancer.
Measurement of ANCA, C-reactive protein, and ESR may help ascertain the activity of this patient’s granulomatosis with polyangiitis. A renal biopsy can diagnose and classify kidney involvement in granulomatosis with polyangiitis. However, this patient has a non-glomerular source for his hematuria and cystoscopy is the diagnostic test of choice.
(Choice D) The detection of dysmorphic red blood cells (cells with blebs or protrusions, so-called “Mickey-Mouse” head RBCs) in the urine is highly suggestive of a glomerular source of hematuria, as is the presence of RBC casts and > 500 mg/day of proteinuria. In this patient, the passage of urinary clots strongly suggests the presence of an extra-glomerular site of bleeding, and cystoscopy should be performed even if dysmorphic urinary RBCs are present.