Internal Medicine Exam Acute Kidney Injury 4 — Questions and Answers
Question 1: A 50-year-old diabetic man develops AKI after starting an ACE inhibitor. Renal artery duplex shows >70% stenosis bilaterally. What is the mechanism of AKI in this patient?
- Direct tubular toxicity from ACE inhibitor
- Loss of efferent arteriolar tone causing drop in glomerular perfusion pressure (Correct answer)
- Immune-mediated interstitial nephritis
- Afferent arteriolar vasoconstriction
Correct answer: Loss of efferent arteriolar tone causing drop in glomerular perfusion pressure
In bilateral renal artery stenosis, glomerular filtration depends on angiotensin II–mediated efferent vasoconstriction; ACE inhibitors remove this compensation, causing GFR to fall precipitously.
Question 2: Which of the following is an ABSOLUTE indication for emergent dialysis in AKI?
- Creatinine >4 mg/dL
- Urine output <0.5 mL/kg/h for 6 hours
- Uremic pericarditis with friction rub (Correct answer)
- BUN >60 mg/dL
Correct answer: Uremic pericarditis with friction rub
Uremic pericarditis is an absolute indication for urgent dialysis, as it indicates severe uremia that can progress to life-threatening pericardial effusion or tamponade.
Question 3: A 65-year-old man with hypertension develops AKI with blood pressure of 240/130 mmHg. Urinalysis shows RBC casts and 3+ proteinuria. LDH is elevated and peripheral smear shows schistocytes. What diagnosis best explains his AKI?
- IgA nephropathy
- Thrombotic microangiopathy (malignant hypertension) (Correct answer)
- Lupus nephritis
- Minimal change disease
Correct answer: Thrombotic microangiopathy (malignant hypertension)
Malignant hypertension causes thrombotic microangiopathy with schistocytes on peripheral smear, hemolysis (elevated LDH), and glomerular injury (RBC casts, proteinuria).
Question 4: Which of the following parameters is used to calculate the Fractional Excretion of Urea (FEUrea), and when is it preferred over FENa?
- Used in all AKI patients; calculated from serum and urine urea and creatinine
- Preferred in patients on diuretics; less affected by diuretic-induced natriuresis than FENa (Correct answer)
- Used only in hypernatremic patients
- Preferred in oliguric AKI regardless of medications
Correct answer: Preferred in patients on diuretics; less affected by diuretic-induced natriuresis than FENa
FEUrea <35% suggests prerenal AKI and is preferred over FENa in patients receiving diuretics, since diuretics artificially raise urine sodium excretion independent of volume status.
Question 5: A 40-year-old woman presents with AKI, bilateral uveitis, and granulomas on biopsy. Which diagnosis should be considered?
- Wegener's granulomatosis (GPA)
- Sarcoidosis with granulomatous interstitial nephritis (Correct answer)
- Goodpasture syndrome
- Alport syndrome
Correct answer: Sarcoidosis with granulomatous interstitial nephritis
Sarcoidosis can cause AKI through granulomatous interstitial nephritis and hypercalcemia-mediated nephrocalcinosis, and is associated with uveitis.
Question 6: A patient in the ICU receives tobramycin for 10 days. On day 8, creatinine begins rising. Urine shows β2-microglobulinuria. What pattern of AKI is expected?
- Proximal tubular necrosis with non-oliguric AKI (Correct answer)
- Oliguric AKI with glomerulonephritis
- Postrenal AKI from crystalluria
- Prerenal AKI from aminoglycoside-induced natriuresis
Correct answer: Proximal tubular necrosis with non-oliguric AKI
Aminoglycosides preferentially accumulate in proximal tubular cells, causing non-oliguric ATN; β2-microglobulinuria reflects proximal tubular dysfunction.
Question 7: After successful kidney transplantation, a recipient develops AKI on day 3 with oliguria and a biopsy showing interstitial edema, lymphocytic infiltration, and tubulitis. What is the most likely cause?
- Calcineurin inhibitor toxicity
- Acute cellular rejection (T-cell mediated) (Correct answer)
- BK virus nephropathy
- Recurrent focal segmental glomerulosclerosis
Correct answer: Acute cellular rejection (T-cell mediated)
Acute cellular rejection occurring days to weeks post-transplant is characterized by tubulitis and lymphocytic interstitial infiltration on biopsy and requires augmented immunosuppression.
Internal Medicine Exam Acute Kidney Injury 4
A 50-year-old diabetic man develops AKI after starting an ACE inhibitor.
Renal artery duplex shows >70% stenosis bilaterally.
What is the mechanism of AKI in this patient?