Acute Kidney Injury – Clinical Scenarios with Lab Data
You will be presented with 12 clinical scenarios of children with suspected acute kidney injury.
For each, interpret the lab data and provide the most likely diagnosis, mechanism, and next step.
Focus on differentiating prerenal azotemia, acute tubular necrosis (ATN), and other causes using urinary indices.
❓ Case 1: 4-year-old with 2 days of vomiting, diarrhea. Labs: BUN 45 mg/dL, Cr 1.0, urine Na 10, FeNa 0.5%, urine osmolality 550. What is the diagnosis and next step?
📊 Lab Data: BUN 45, Cr 1.0, Na 135, K 3.8, Cl 100, HCO3 20. Urine Na 10, FeNa 0.5%, Uosm 550.
✅ Model Answer:
• Diagnosis: Prerenal azotemia secondary to dehydration (vomiting/diarrhea).
• Evidence: FeNa 0.5% (<1%), Uosm 550 (>500), BUN:Cr ratio 45:1 (>20).
• Next step: IV fluid bolus (20 mL/kg normal saline), monitor urine output and Cr.
❓ Case 2: 7-year-old with septic shock, oliguria. Labs: Cr 2.5 (baseline 0.6), urine Na 45, FeNa 3.2%, urine osmolality 320, muddy-brown casts on UA. What is the diagnosis?
📊 Lab Data: Cr 2.5, BUN 30, Na 138, K 5.2, HCO3 16. Urine Na 45, FeNa 3.2%, Uosm 320. UA: muddy-brown granular casts.
✅ Model Answer:
• Diagnosis: Acute tubular necrosis (ATN) – ischemic secondary to septic shock.
• Evidence: FeNa 3.2% (>2%), Uosm 320 (<350), BUN:Cr ratio ~12:1 (<15), muddy-brown casts.
• Next step: Supportive care – maintain perfusion, avoid nephrotoxins, monitor for dialysis.
❓ Case 3: 10-year-old with crush injury, dark urine. Labs: Cr 2.0, K 5.8, urine dipstick +blood but no RBCs. What is the diagnosis and treatment?
📊 Lab Data: Cr 2.0, BUN 28, Na 140, K 5.8, Ca 7.5, Phos 6.5. UA: +blood, no RBCs, myoglobin casts.
✅ Model Answer:
• Diagnosis: Rhabdomyolysis-induced ATN (myoglobinuria).
• Evidence: Crush injury, dark urine, +blood on dipstick but no RBCs = myoglobinuria. Hyperkalemia, hyperphosphatemia.
• Next step: Aggressive IV hydration, alkalinize urine (sodium bicarbonate), monitor K (calcium gluconate if ECG changes). Consider dialysis if severe.
❓ Case 4: 5-year-old with nephrotic syndrome, edema, oliguria. Labs: Cr 1.8, urine Na 8, FeNa 0.3%, proteinuria 4+. What is the mechanism of AKI?
📊 Lab Data: Cr 1.8, BUN 35, albumin 1.8, urine Na 8, FeNa 0.3%, Uosm 480. UA: 4+ protein.
✅ Model Answer:
• Diagnosis: Prerenal azotemia secondary to intravascular volume depletion (nephrotic syndrome).
• Evidence: FeNa 0.3% (<1%), Uosm 480, BUN:Cr ~19:1. Low intravascular volume due to low oncotic pressure.
• Next step: Albumin infusion (25%) followed by furosemide if needed. Monitor Cr, urine output.
❓ Case 5: 6-year-old on gentamicin for 5 days, oliguria. Labs: Cr 2.2 (baseline 0.5), urine Na 50, FeNa 4%, urine osmolality 280. What is the diagnosis?
📊 Lab Data: Cr 2.2, BUN 32, Na 136, K 5.0, HCO3 18. Urine Na 50, FeNa 4%, Uosm 280. UA: granular casts, RTE cells.
✅ Model Answer:
• Diagnosis: Nephrotoxic ATN due to aminoglycoside (gentamicin).
• Evidence: FeNa 4% (>2%), Uosm 280 (<350), BUN:Cr ~14:1 (<15), renal tubular epithelial cells.
• Next step: Stop gentamicin, supportive care. Monitor Cr, electrolytes. Consider dialysis if severe.
❓ Case 6: 8-year-old with hypertension, oliguria. Labs: Cr 2.0, urine Na 12, FeNa 0.8%, RBC casts. What is the mechanism of AKI?
📊 Lab Data: Cr 2.0, BUN 38, Na 138, K 4.5. UA: RBC casts, dysmorphic RBCs, protein 2+. Urine Na 12, FeNa 0.8%, Uosm 420.
✅ Model Answer:
• Diagnosis: Acute glomerulonephritis (post-strep GN) – intrinsic AKI.
• Evidence: RBC casts, dysmorphic RBCs, proteinuria. FeNa 0.8% (<1%) – due to reduced GFR and intact tubular reabsorption.
• Next step: Manage hypertension, fluid restriction, diuretics. Monitor Cr, complement levels. Dialysis if severe fluid overload or uremia.
❓ Case 7: 3-year-old with HUS (diarrhea-associated), oliguria, pallor. Labs: Cr 3.0, urine Na 40, FeNa 2.5%, UA: protein, RBCs. What is the diagnosis?
✅ Model Answer:
• Diagnosis: Hemolytic uremic syndrome (HUS) causing ATN – microvascular thrombosis.
• Evidence: Hemolysis (Hb 6.5, LDH↑, haptoglobin↓), thrombocytopenia, AKI. FeNa 2.5% (>2%) – ischemic ATN.
• Next step: Supportive care – fluid management, dialysis if needed. Monitor complications. Consider eculizumab in atypical HUS.
❓ Case 8: 12-year-old with sepsis, anuria for 2 days. Labs: Cr 4.0, K 6.8, pH 7.1, HCO3 10, FeNa 3%. What is the most urgent next step?
📊 Lab Data: Cr 4.0, BUN 60, K 6.8, Na 134, pH 7.1, HCO3 10, FeNa 3%, Uosm 300. UA: muddy-brown casts.
✅ Model Answer:
• Diagnosis: Severe ATN with hyperkalemia and metabolic acidosis – indications for dialysis.
• Immediate: IV calcium gluconate (cardioprotection), insulin/glucose, albuterol for hyperkalemia. Sodium bicarbonate if pH <7.1.
• Next step: Start dialysis (hemodialysis or PD) – AEIOU: Acidosis, Electrolytes (K >6.5), Overload, Uremia.
❓ Case 9: 9-year-old with contrast study, oliguria 24h later. Labs: Cr 2.0 (baseline 0.7), urine Na 35, FeNa 2.8%. What is the diagnosis and prevention?
📊 Lab Data: Cr 2.0, BUN 28, Na 137, K 4.2. Urine Na 35, FeNa 2.8%, Uosm 320. UA: granular casts.
✅ Model Answer:
• Diagnosis: Contrast-induced nephropathy (ATN).
• Evidence: Recent contrast study, FeNa 2.8% (>2%), Uosm 320 (<350).
• Prevention: IV hydration with normal saline (or sodium bicarbonate) before contrast. Limit contrast volume, avoid NSAIDs, minimize nephrotoxins.
❓ Case 10: 2-year-old with oligurea, urine output now 3 mL/kg/hr, Cr falling from 3.0 to 1.5. What phase is this and what complication must be monitored?
📊 Lab Data: Cr 1.5 (falling from 3.0), urine output 3 mL/kg/hr, Na 140, K 3.8. Previously oliguric.
✅ Model Answer:
• Diagnosis: Recovery (diuretic) phase of ATN.
• Evidence: Increasing urine output (polyuria), falling Cr – recovery phase.
• Monitor: Risk of hypovolemia and electrolyte losses (Na, K, Ca, Mg). Replace losses (mL for mL), monitor electrolytes, prevent dehydration.
❓ Case 11: 11-year-old with leukemia on chemotherapy (cisplatin), oliguria. Labs: Cr 2.5, Mg 1.0, K 3.0, urine Na 45, FeNa 3.5%. What is the diagnosis?
📊 Lab Data: Cr 2.5, BUN 35, Mg 1.0, K 3.0, Ca 8.5. Urine Na 45, FeNa 3.5%, Uosm 290.
✅ Model Answer:
• Diagnosis: Nephrotoxic ATN secondary to cisplatin.
• Evidence: Chemotherapy with cisplatin, FeNa 3.5% (>2%), Uosm 290 (<350), hypomagnesemia (classic).
• Next step: Hydration, avoid nephrotoxins. Monitor Mg (supplement), K, Ca. Consider dialysis if severe.
❓ Case 12: 6-month-old with obstructive uropathy (posterior urethral valves), anuria. Labs: Cr 2.8, urine Na 15, FeNa 0.4%. What is the mechanism of AKI?
📊 Lab Data: Cr 2.8, BUN 40, Na 138, K 5.0. Urine Na 15, FeNa 0.4%, Uosm 420. USG: hydronephrosis.
✅ Model Answer:
• Diagnosis: Postrenal AKI due to obstruction (posterior urethral valves).
• Evidence: Hydronephrosis on USG, FeNa 0.4% (<1%) – tubular reabsorption intact despite obstruction.
• Next step: Relieve obstruction (bladder catheterization, valve ablation). Monitor post-obstructive diuresis (risk of dehydration).
⚡ Quick FCPS‑style MCQ
A child with AKI has FeNa 0.3%, urine osmolality 550, BUN:Cr 25:1. The most likely diagnosis is: