Case 18: Diagnostic Testing

Case 18 Index

Take a look at some initial diagnostic testing below.
Urinalysis/microscopy, urine electrolytes
Urine sediment
Basic labs
Kidney Ultrasound

Basic Lab Ref

Update your differential diagnosis (choose 3)!
Post-infectious glomerulonephritis (PIGN)
Membranous nephropathy
Atheroembolic disease
Warfarin-induced skin necrosis
Hepatitis-C associated membranoproliferative glomerulonephritis (MPGN)
Eosinophilic granulomatosis with polyangiitis
Granulomatosis with polyangiitis
Acute interstitial nephritis (AIN)
Systemic lupus erythematosus (SLE) nephritis
IgA nephropathy
Anti-glomerular basement membrane (GBM) disease
Acute tubular necrosis (ATN)

Let’s start our extended work-up below!

Choose the 5 highest yield diagnostic tests.
Complement levels (C3, C4)
We should look for complement-mediated diseases in patients like this one with nephritic syndrome. In this case, complements are normal with C3 109 mg/dL (ref: 90 – 180 mg/dL) and C4 14 mg/dL (ref: 10 – 40 mg/dL)
HIV nephropathy is more likely to present with a nephrotic rather than nephritic syndrome, so this may be low yield. Try another test!
Urine eosinophils
This is a low yield test given this patient’s presentation. Further, this is not a sensitive or specific test though it has been traditionally used to look for acute interstitial nephritis.
Hemoglobin A1C
Diabetic nephropathy is unlikely to present with a nephritic  as our patient has here. Try again!
Anti-glomerular basement membrane antibody
You call the lab, and the result for this test will take 1 week. We’ll have to move on for now and try another test.
Anti-nuclear antibody (ANA)
1:60 (reference: less than 1:80). Systemic lupus erythematosus (SLE) nephritis is possible given this patient’s nephritic syndrome, but this clinical presentation makes other diagnoses more likely.
Hepatitis C antibody
Hepatitis C-associated glomerulonephritis can definitely present like this. The antibody test is negative.
Anti-neutrophil cytoplasmic antibody (ANCA screen)
The c-ANCA titer is elevated, the p-ANCA titer is within normal limits. 
Serum protein electrophoresis and free light chains
Patients with monoclonal gammopathies and kidney disease typically present with nephrotic syndrome – this is likely a low yield test for now Choose another!

Click here to perform the biopsy!

Case 18 Index
Case 18 Introduction
Case 18 Physical Exam