Internal Medicine Acute Kidney Injury Questions and Answers — Questions and Answers
Question 1: A 75-year-old man with heart failure is admitted with decompensation and treated aggressively with intravenous furosemide. His baseline creatinine was 1.2 mg/dL. On day 3, his creatinine is 2.5 mg/dL and his urine output is low. His blood pressure is 105/65 mmHg. Which set of urine findings is most consistent with pre-renal azotemia from over-diuresis?
- Urine Sodium > 40 mEq/L, FeNa > 2%, muddy brown casts
- Red blood cell casts, proteinuria > 1 g/day
- Urine Sodium < 20 mEq/L, FeNa < 1%, bland sediment (Correct answer)
- White blood cell casts, urine eosinophils > 5%
Correct answer: Urine Sodium < 20 mEq/L, FeNa < 1%, bland sediment
Pre-renal azotemia is caused by decreased renal perfusion. In response, the healthy tubules avidly reabsorb sodium and water to conserve volume. This leads to concentrated urine with a low urine sodium (<20 mEq/L) and a fractional excretion of sodium (FeNa) less than 1%. The sediment is typically bland or may show hyaline casts. Muddy brown casts are pathognomonic for Acute Tubular Necrosis (ATN). RBC casts suggest glomerulonephritis. WBC casts and eosinophils suggest Acute Interstitial Nephritis (AIN).
Question 2: A 45-year-old male is found down after a reported seizure. He is confused with diffuse muscle tenderness. His creatinine is 2.1 mg/dL, and a urine dipstick is strongly positive for blood but microscopic analysis shows 0-2 RBCs/hpf. His creatine kinase (CK) level is 45,000 U/L. What is the most critical initial step in managing his acute kidney injury?
- Administration of sodium bicarbonate to alkalinize the urine
- Aggressive intravenous fluid resuscitation with isotonic saline (Correct answer)
- Urgent hemodialysis
- Administration of N-acetylcysteine
Correct answer: Aggressive intravenous fluid resuscitation with isotonic saline
The patient has rhabdomyolysis-induced AKI, evidenced by the high CK and myoglobinuria (positive blood on dipstick with no RBCs). The cornerstone of management is early and aggressive intravenous fluid resuscitation with isotonic crystalloids to increase urine flow, flush out myoglobin casts, and prevent further renal tubular injury. While urine alkalinization is sometimes considered, it is secondary to and should not delay aggressive volume repletion. Dialysis is reserved for severe complications like refractory hyperkalemia or fluid overload, and N-acetylcysteine has no role.
Question 3: A 68-year-old male with a baseline creatinine of 1.8 mg/dL and diabetes mellitus is scheduled for a cardiac catheterization requiring intra-arterial contrast. Which of the following interventions has the strongest evidence for preventing contrast-induced acute kidney injury (CI-AKI)?
- Intravenous isotonic saline infusion before and after the procedure (Correct answer)
- Oral N-acetylcysteine 24 hours before and on the day of the procedure
- Intravenous sodium bicarbonate infusion
- A single dose of intravenous furosemide immediately after the procedure
Correct answer: Intravenous isotonic saline infusion before and after the procedure
The most effective and evidence-based strategy for preventing CI-AKI in high-risk patients is periprocedural volume expansion with intravenous isotonic crystalloids, such as 0.9% saline. This maintains renal perfusion and tubular flow. While sodium bicarbonate has been studied, its superiority over saline is not definitively established. N-acetylcysteine has shown conflicting results and is not consistently recommended. Furosemide is contraindicated as it can cause volume depletion and worsen kidney injury.
Question 4: A 58-year-old male with decompensated alcoholic cirrhosis and ascites is hospitalized. His baseline creatinine of 0.9 mg/dL has risen to 2.5 mg/dL over two days. He is not in shock, has not received nephrotoxic drugs, and a renal ultrasound is normal. Urine sodium is < 10 mEq/L. After a 2-day trial of diuretic cessation and volume expansion with 1 g/kg of albumin, his creatinine does not improve. Which of the following is the most appropriate next step in management?
- Initiation of broad-spectrum antibiotics for presumed SBP
- Placement of a transjugular intrahepatic portosystemic shunt (TIPS)
- Administration of midodrine, octreotide, and continued albumin (Correct answer)
- Urgent renal replacement therapy
Correct answer: Administration of midodrine, octreotide, and continued albumin
This patient meets the diagnostic criteria for Hepatorenal Syndrome-Acute Kidney Injury (HRS-AKI). After ruling out other causes and failing to respond to a trial of albumin expansion, the standard of care is medical therapy with splanchnic vasoconstrictors (octreotide) and a systemic vasoconstrictor (midodrine), along with continued albumin. This combination counteracts the splanchnic vasodilation and improves renal perfusion. TIPS and dialysis are second-line or bridging therapies to liver transplantation, which is the definitive treatment.
Question 5: A 62-year-old female with severe acute kidney injury (creatinine 6.8 mg/dL) secondary to sepsis is being managed in the ICU. Which of the following findings is the most urgent indication for initiating renal replacement therapy?
- Blood urea nitrogen (BUN) of 110 mg/dL
- Serum potassium of 6.3 mEq/L, refractory to medical therapy
- Pericardial friction rub on auscultation (Correct answer)
- Serum bicarbonate of 16 mEq/L
Correct answer: Pericardial friction rub on auscultation
The classic indications for urgent dialysis are remembered by the mnemonic AEIOU: Acidosis (severe), Electrolytes (refractory hyperkalemia), Intoxications, Overload (refractory), and Uremia (symptomatic). A pericardial friction rub is a sign of uremic pericarditis, a life-threatening complication of uremia, and is an absolute indication for immediate dialysis. While refractory hyperkalemia is also an urgent indication, uremic pericarditis represents severe end-organ toxicity requiring the most emergent intervention. An elevated BUN or moderate acidosis alone are not absolute indications.
Question 6: A 70-year-old male was started on omeprazole and piperacillin-tazobactam one week ago for aspiration pneumonia. He now presents with a new-onset maculopapular rash, a temperature of 38.5°C (101.3°F), and a rise in his serum creatinine from a baseline of 1.1 mg/dL to 3.0 mg/dL. Urinalysis is most likely to show which of the following findings?
- Muddy brown granular casts
- White blood cell casts and sterile pyuria (Correct answer)
- Hyaline casts and a fractional excretion of sodium <1%
- Red blood cell casts and dysmorphic RBCs
Correct answer: White blood cell casts and sterile pyuria
The clinical triad of fever, rash, and rising creatinine after exposure to a new drug is highly suggestive of drug-induced acute interstitial nephritis (AIN). The characteristic urinalysis finding in AIN is sterile pyuria (white blood cells in the absence of bacteria) and white blood cell casts, indicating inflammation within the renal interstitium. While urine eosinophils are classic, they are not always present. The other options suggest ATN (A), pre-renal disease (C), or glomerulonephritis (D).
