Question

What is the likely source of hematuria that has been persisting for the past 3 days, with red cell casts evident on urinalysis?

• A. Bladder
• B. Urethra
• C. Kidney
• D. Ureter

Hint:

Only kidney tubules can mould red blood cells into a cast.

Answer 1

The Correct Option is C

Step 1: Recall what a red cell cast actually is.
A cast is a cylindrical plug that forms inside the kidney's tubules, moulded by the tubule's own shape. Red cell casts form only when red blood cells get trapped inside this tubular mould before being washed out into the urine.

Step 2: Work out where that mould can happen.
Tubules exist only inside the kidney (nephron). The bladder, ureter, and urethra are just hollow tubes lined by transitional or squamous cells; they have no tubular structure that could shape a cast.

Step 3: Apply this to the case.
Since red cell casts can only be made inside kidney tubules, their presence tells us the red blood cells entered the urine at the level of the kidney (glomerulus or tubule), not lower down in the urinary tract.

Step 4: Rule out the other options.
Bladder bleeding (from a stone, infection, or tumour) gives free red cells or clots, never true casts.
Ureteric bleeding also gives plain blood, since urine simply flows through the ureter without a tubular mould.
Urethral bleeding shows as blood at the start of urination or at the meatus, again with no casts.

Step 5: Final answer.
Red cell casts point specifically to a renal (glomerular) source of bleeding.
\[ \boxed{\text{Kidney}} \]