Case 8: Diagnostic Testing

Case 8 Index

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

Basic Lab Ref

Find the 2 highest yield tests below!
Urine sediment
Excellent choice! The urine sediment can often provide clues to the etiology of a patient’s kidney disease.
Urine protein to urine creatinine ratio (UPCR)
Great!  The urine protein to  urine creatinine ratio is 10, which tells us that this patient is excreting approximate 10 grams of protein in the urine over 24 hours (nephrotic range proteinuria!). Though the urinalysis gives us an estimate of the degree of albuminuria, proteinuria should be quantified when present.  Further, the urinalysis does NOT detect non-albumin proteins, like immunoglobulins which may be present in the urine in other disease states. Of note, this test is most accurate when the patient’s serum creatinine is at steady state (or not changing day to day).
Complement levels (C3, C4)
This might be a low yield test here, given the urinalysis findings. Complement levels should be investigated in patients with signs and symptoms suggestive of nephritic syndrome. Try again!
Urine eosinophils
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. Pick again!
Creatine phosphokinase (CPK)
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 is negative for blood. Try another test!
Hemoglobin A1C
Though diabetic nephropathy (DN) often presents with albuminuria, it would be unusual for a young patient to develop sudden onset of nephrotic syndrome due to DN. Diabetic nephropathy more commonly presents after the disease has been present for several years, thus this kidney disease would be less likely in a 7 year old without known history of diabetes. Let’s try again!
Update your differential diagnosis before moving on! (choose 3)!
Membranous nephropathy
Henoch-Schonlein purpura
Focal segmental glomerulosclerosis
Acute interstitial nephritis (AIN)
Sickle cell nephropathy
Systemic lupus erythematosus (SLE) nephritis
Minimal change disease
Acute tubular necrosis (ATN)
IgA nephropathy
Hepatitis C-related glomerulonephritis
Post-infectious glomerulonephritis

You talk to the patient’s parents and counsel them on the importance of obtaining a kidney biopsy. Together, you talk with the patient and explain the important next steps. His older sister comes to the hospital for support, and you plan to proceed.

Click here to perform the biopsy!

Case 8 Index
Case 8 Introduction
Case 8 Physical Exam