What is the management approach for a patient with a Blood Urea Nitrogen (BUN) to creatinine ratio of 28, indicating potential prerenal acute kidney injury (AKI)?

Management of BUN/Creatinine Ratio of 28

A BUN/creatinine ratio of 28 indicates prerenal acute kidney injury (AKI), and you should immediately withdraw diuretics and nephrotoxic medications, assess volume status, and initiate volume expansion with isotonic crystalloids or albumin (1 g/kg for 2 days if creatinine has doubled from baseline). 1

Immediate Assessment and Risk Stratification

Determine the cause of AKI by obtaining:

• Baseline creatinine from the previous 3 months (if unavailable, use admission creatinine as baseline) 1
• Complete medication review focusing on NSAIDs, ACE inhibitors, ARBs, aminoglycosides, diuretics, and contrast agents 1, 2
• Volume status assessment through physical examination for signs of hypovolemia (dry mucous membranes, decreased skin turgor, orthostatic hypotension) or volume overload 1
• Urinalysis with microscopy to exclude hematuria, proteinuria, or abnormal sediment suggesting intrinsic renal disease 1

Calculate fractional excretion of sodium (FENa <1%) and fractional excretion of urea (FEUrea <28.16%) to confirm prerenal etiology 2, 3

Stage the AKI severity using KDIGO criteria:

• Stage 1: Creatinine increase ≥0.3 mg/dL within 48 hours OR ≥1.5× baseline within 7 days 1
• Stage 2: Creatinine increase 2.0-2.9× baseline 1
• Stage 3: Creatinine increase ≥3× baseline OR ≥4.0 mg/dL OR need for renal replacement therapy 1

Immediate Interventions for Prerenal AKI

Stop all nephrotoxic medications immediately:

• Discontinue NSAIDs (increase AKI risk more than twofold in volume-depleted patients) 1, 4
• Withdraw all diuretics regardless of AKI stage 1, 2
• Hold ACE inhibitors and ARBs (impair renal autoregulation) 1, 2, 4
• Discontinue aminoglycosides and other nephrotoxins 1, 4
• Stop nonselective beta-blockers 1

Initiate volume expansion based on clinical assessment:

• For hypovolemic AKI: Administer isotonic crystalloids (normal saline or Ringer's lactate) as first-line therapy 2, 4
• For patients with doubling of serum creatinine: Give albumin 1 g/kg (maximum 100g) for two consecutive days 1
• Avoid starch-containing colloid solutions (associated with harm in AKI) 4

Infection Screening

Perform rigorous search for infection in all AKI patients:

• Obtain blood cultures, urine cultures, and chest radiograph 1, 2
• In cirrhotic patients: Perform diagnostic paracentesis to evaluate for spontaneous bacterial peritonitis 1
• Start broad-spectrum antibiotics when infection is strongly suspected (do not use routine prophylactic antibiotics) 1, 2

Monitoring and Response Assessment

Monitor daily:

• Serum creatinine and electrolytes (particularly potassium and bicarbonate) 1, 2, 4
• Urine output with goal >0.5 mL/kg/hour 1, 4
• Volume status using vital signs, urine output, and when indicated, echocardiography or CVP 1

Define treatment response:

• Full response: Return of creatinine to within 0.3 mg/dL of baseline 1
• Partial response: Regression of AKI stage but creatinine remains ≥0.3 mg/dL above baseline 1
• No response: No regression of AKI stage 1

Management of Non-Responsive AKI

If creatinine remains >2× baseline despite 2 days of diuretic withdrawal and volume expansion:

• Consider hepatorenal syndrome (HRS-AKI) if patient has cirrhosis with ascites, no shock, no nephrotoxic drug use, and absence of proteinuria >500 mg/day or microhematuria 1
• Initiate vasoconstrictor therapy with albumin: terlipressin 1 mg every 4-6 hours (increase to 2 mg if no 25% creatinine reduction by day 3) OR norepinephrine 0.5 mg/h continuous infusion (titrate by 0.5 mg/h every 4 hours to maximum 3 mg/h) 1
• Continue albumin 20-40 g daily with vasoconstrictors 1

Common Pitfalls to Avoid

Do not delay fluid resuscitation while waiting for laboratory confirmation - clinical assessment of volume status should guide immediate treatment 2

Do not use estimated GFR (eGFR) for medication dosing in AKI - it overestimates true renal function; calculate creatinine clearance using Cockcroft-Gault formula instead 5

Monitor closely for fluid overload complications - excessive albumin administration can cause life-threatening pulmonary edema 1

Adjust serum creatinine interpretation in volume-overloaded patients - significant IV fluid administration causes dilutional effect that may mask true GFR reduction 1

Follow-Up and Long-Term Management

Evaluate kidney function 3 months after AKI episode:

• Assess for resolution, new-onset CKD, or worsening of pre-existing CKD 1, 4
• Monitor serum creatinine every 2-4 weeks for 6 months after discharge to detect recurrent AKI 1, 4
• Target high-risk populations: Stage 3 AKI, incomplete recovery at discharge, or baseline CKD 1, 4