Case 42: Diagnostic Testing

Case 42 Index

Additional diagnostic testing is obtained by the ICU team.
Basic Labs
Baseline serum creatinine is 0.8-0.9mg/dl, most recently 0.85mg/dL two weeks prior.
Urinalysis, urine electrolytes
Kidney/bladder ultrasound
Both kidneys appears normal, without evidence of hydronephrosis or hydroureter. The echogenicity is normal. The left kidney measures 9.5 cm and the right kidney measures 10.1 cm.
Urine sediment
Chest X-Ray

(Image courtery of A. Prof Frank Gaillard from Case 35985)

Basic Lab Ref

What is the most likely cause of this patient’s acute kidney injury (AKI)?
Acute tubular necrosis (ATN)
Correct! This patient is oliguric, with many “muddy brown” granular casts on urine sediment. A FENa > 1.0% is also suggestive, though should not be considered in isolation.
Obstructive uropathy
With a normal appearing kidney/bladder ultrasound and a foley catheter in place, this patient’s low urine output and AKI are likely due to something else. Try again!
This patient has been volume resuscitated and continues to worsen, suggesting against Pre-renal AKI. He also has significant abnormalities on urine sediment. Try again!
Rapidly progressive glomerulonephritis (RPGN)
In the absence of red blood cells on urinalysis, it is unlikely for this patient to have glomerulonephritis. Take another look at the urine sediment; what kind of casts are those?
Cardiorenal syndrome
While this patient does have hypotension and evidence of volume overload after aggressive fluid resuscitation, his urine studies and urine sediment suggest a different cause of oliguric AKI. Try again!

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Case 42 Index
Case 42 Introduction
Case 42 Physical Exam