Case 7: Diagnostic Testing

Case 7 Index

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

Basic Lab Ref

Select the most high yield next tests to continue the work-up below!
Anti-nuclear cytoplasmic antibody (ANCA) screen
Negative, but a good thought! ANCA-associated vasculitis typically presents as a rapid progressively glomerulonephritis (RPGN), and while it typically affects individuals older than 50 years old, it can present with a nephritic syndrome at any age.
Complement levels (C3, C4)
C3 6 mg/dL (ref: 90 – 180 mg/dL); C4 8 mg/dL (ref: 10 – 40 mg/dL). Great choice, we should look for complement-mediated diseases in patients like this with a nephritic picture.
Anti-phospholipase A2 receptor (PLA2R) antibody
This test is low yield here. Our patient is presenting with a nephritis, and anti-PLA2R is more helpful to narrow our differential of nephrotic syndrome.
Anti-nuclear antibody (ANA)
1:1080 (reference <1:80). Yikes! This patient has a significantly elevated ANA titer, which can help us narrow our differential further.
Rheumatoid factor (RF)
<5 IU/mL (reference <14IU/mL). It is not unreasonable to send this test in search of a cryoglobulinemic glomerulonephritis, though it may be less likely in this case.
Bone marrow biopsy
You’ve clearly picked up on this patient’s cytopenias (low cell counts). However, a bone marrow biopsy is an invasive test and might not give us the diagnosis. For now, our colleagues in hematology advise other diagnostic tests to help this patient.
Anti-streptolysin O (ASO) titer
Negative, but a reasonable test to have sent in this young patient presenting with evidence of nephritis, particularly given her recent febrile illness.
What’s risen to the top of your differential diagnosis? Choose 3!
Membranous nephropathy
Post-infectious glomerulonephritis
Acute interstitial nephritis (AIN)
ANCA-associated glomerulonephritis
Systemic lupus erythematosus (SLE) nephritis
Minimal change disease
Acute tubular necrosis (ATN)
IgA nephropathy
Hepatitis C-related glomerulonephritis
Anti-glomerular basement membrane (GBM) disease

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Case 7 Index
Case 7 Introduction
Case 7 Physical Exam