Case 41: Diagnostic Testing

Case 41 Index

In the clinic, you perform some additional diagnostic tests:
Basic Labs
Urinalysis/microscopy, urine electrolytes

Basic Lab Ref


Choose the highest-yield tests below (many of these will be helpful)!
Kidney/Bladder Ultrasound
Great choice! Here’s an image of the right kidney. It measures 14 cm across. (Image courtesy Dr. Julius Rozmiarek, from the Case 62615)
HIV viral load and CD4 count
It is important to assess this patient’s HIV viral load, which can increase his risk for certain types of kidney disease. His viral load is >1,000,000 copies/mL, and CD4 count is 120 cells/uL.
ANCA titers
This would be a good choice for a patient with nephritic syndrome. Try again!
Hepatitis B and C serologies
Great choice! It is important to assess for HCV and/or HBV co-infection, as these viruses can lead to a variety of kidney pathology. This patient tests negative for HBV and HCV.
Rapid plasma reagin (RPR) test
Nice! This test can identify syphilis infection, which is an important cause of secondary membranous nephropathy and nephrotic syndrome.
Anti-PLA2R antibody titer
Absolutely! This is a useful test in a patient with nephrotic range proteinuria. An elevated antibody titer would be consistent with membranous nephropathy and, some would argue, could spare the patient a kidney biopsy. This will take approximately 1 week to result.
Urine eosinophils (Hansel’s stain)
Hm…this test has a low sensitivity, and its positive predictive value for acute interstitial nephritis (AIN) is only about 40%. Pick again!
Serum protein electrophoresis (SPEP) and free light chains
This is a reasonable test for a patient with nephrotic range proteinuria to assess for a monoclonal gammopathy, though his younger age makes this less likely. His SPEP shows hypergammaglobulinemia without an M-spike, and serum free light chains are within normal. Monoclonal gammopathies can lead to variety of glomerular diseases that cause nephrotic range proteinuria including amyloidosis and light chain deposition disease (LCDD).
Based on the information we have thus far, what are the top three diagnoses on your differential?
Systemic lupus erythematous (SLE) nephritis
Diabetic nephropathy
HIV-associated nephropathy (HIVAN)
HIV-associated immune complex kidney Disease (HIVICK)
Hepatitis C- associated glomerular disease
Primary membranous nephropathy
Minimal change disease (MCD)
IgA nephropathy
Acute interstitial nephritis (AIN)
Hypertensive nephropathy
Tubular dysfunction due to tenofovir

We need a kidney biopsy to make the diagnosis here! Click here to perform a percutaneous biopsy.

Case 41 Index
Case 41 Introduction
Case 41 Physical Exam