Excellent choice! Hematuria should be differentiated as glomerular or non-glomerular if possible, by looking at the urine sediment. What do you see?

Negative. Though ANCA-associated vasculitis typically presents as a rapid progressively glomerulonephritis (RPGN) and affects individuals older than 50 years old, it can occur at any age and may present with a nephritic syndrome.

Both C3 and C4 are within normal limits. Complement levels should be investigated in patients with nephritic syndrome.

This is a low yield test here. Traditionally, this test has been described for acute interstitial nephritis (AIN) – though the sensitivity and specificity for AIN is also poor.

Before moving to an invasive test like this one, we should try to find out whether the hematuria is glomerular or non-glomerular. The cystoscopy would let us look for a bladder malignancy, which might cause non-glomerular hematuria. Let’s try a higher yield test!

The CPK can be markedly elevated in patients with rhabdomyolysis, or breakdown of muscle that can subsequently lead to acute kidney injury. Classically, the urine of these patients is positive for “blood” on the urine dipstick, without the presence of red blood cells. Here, the dipstick reads positive for “blood” due to myoglobinuria.

You consult your hematology colleagues and they advise against a bone marrow biopsy as there are no significant complete blood count (CBC) abnormalities. They advise other diagnostic tests to help this patient.

Diabetic nephropathy presents with albuminuria, not hematuria. Though this patient should be screened for diabetes given his weight, this test is unlikely to be a high yield diagnostic test here.