Case 48: Diagnostic Testing

Case 48 Index

Take a look at this patient’s most recent labs in the Emergency Department.
Basic labs
Urinalysis
Urine sediment

 

Basic Lab Ref

What’s the most likely etiology of this patient’s AKI?
Volume depletion
Acute tubular necrosis
Diabetic nephropathy
Crystal nephropathy due to valganciclovir 
Acute interstitial nephritis
Infection-related glomerulonephritis
Membranous nephropathy
Thin membrane disease
Autosomal dominant polycystic kidney disease (ADPKD)
Urinary tract infection (UTI)
Myeloma cast nephropathy
Lymphoma
Tuberculosis

A kidney ultrasound is performed and does not show stones, cysts, or evidence of hydronephrosis.

Choose the highest yield tests below (more than one choice may be correct)!
Kidney biopsy
We may want to revisit this later, but not so fast! Take a closer look at the data we have so far.
Hemoglobin A1C
This is a reasonable test in a patient with an acute kidney injury and history of diabetes mellitus. The A1C is 6.5%.
Urine culture
Though this patient does not have urinary symptoms, this is a reasonable test here given the pyuria. The urine culture does not grow any organisms.
Intact parathyroid hormone (iPTH), vitamin D-25 OH
Good eye Рthis patient has hypercalcemia. The iPTH level is < 5 pg/mL. The vitamin D-25OH level is 21 ng/mL (normal 20 Р40 ng/mL) 
Vtamin-D 1,25 OH
Great! The vitamin-D 1,25 OH (calcitriol) level is 70 pg/mL (25 – 65 pg/mL).
Serum free light chains & serum immunofixation (IFE)
Not a bad idea for this patient with hypercalcemia. There is no monoclonal protein detected and free light chains are within normal limits, with a normal kappa to lambda ratio.
Chest x-ray
Good choice! Image courtesy of Dr Mohammad Taghi Niknejad (Radiopaedia)
Urine eosinophils
Even though this is a cheap, non-invasive test, the utility of this test is very low for this patient. Give it another shot!
Hepatitis B virus, hepatitis C virus, and human immunodeficiency virus (HIV) serologies
These viruses may be associated with various glomerular diseases – these serologies may not be the most helpful tests here. Try again!
With our new data, what’s your most likely diagnosis now?
Volume depletion
Acute tubular necrosis
Diabetic nephropathy
Crystal nephropathy due to valganciclovir 
Acute interstitial nephritis
Infection-related glomerulonephritis
Membranous nephropathy
Thin membrane disease
Autosomal dominant polycystic kidney disease (ADPKD)
Urinary tract infection (UTI)
Myeloma cast nephropathy

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Case 48 Index
Case 48 Introduction
Case 48 Physical Exam