BUN/Creatinine Ratio

Restore Hydration (if Ratio >20 from Dehydration)

• Oral rehydration: Increase fluid intake to 2-3 liters daily if mild dehydration. Electrolyte solutions (Pedialyte, sports drinks) if vomiting or diarrhea
• IV fluid resuscitation: If severe dehydration with orthostatic symptoms, may need IV normal saline or lactated Ringer's. Typically 1-2 liters over 2-4 hours
• Monitor response: Recheck BUN, creatinine, ratio 12-24 hours after rehydration. Ratio should normalize if dehydration was cause
• Identify cause: Recent illness (vomiting, diarrhea), inadequate intake, diuretics, heat exposure
• Prevent recurrence: Ensure adequate daily fluid intake (30-35 ml/kg). Adjust diuretics if contributing. Educate on signs of dehydration

Evaluate and Treat GI Bleeding (if Ratio >30)

• Assess for bleeding: Check for melena (black tarry stools), hematemesis (vomiting blood), orthostatic vital signs, tachycardia, pallor
• Hemoglobin check: Acute bleeding may not drop Hgb immediately (takes hours). Serial Hgb monitoring if suspected
• Upper endoscopy (EGD): If upper GI bleeding suspected. Identifies and treats ulcers, varices, gastritis, Mallory-Weiss tears
• Stop contributing factors: Discontinue NSAIDs, aspirin, anticoagulants if possible. Start proton pump inhibitor (PPI) 40-80 mg twice daily
• Volume resuscitation: IV fluids, blood transfusion if Hgb <7-8 g/dL or hemodynamically unstable
• Colonoscopy: If lower GI source suspected (though lower GI bleeding elevates ratio less)

Address Intrinsic Kidney Disease (if Ratio 10-20 with Elevated Absolute Values)

Normal ratio (10-20) with both BUN and creatinine elevated indicates intrinsic kidney disease, not pre-renal:

• Identify cause: Diabetes, hypertension, glomerulonephritis, drug toxicity, obstruction
• ACE inhibitors or ARBs: If proteinuria or diabetes present. Slow CKD progression
• SGLT2 inhibitors: Empagliflozin, dapagliflozin for diabetic kidney disease or CKD with albuminuria
• Blood pressure control: Treat to the blood pressure target your clinician sets, which is usually lower with significant proteinuria
• Nephrology referral: If eGFR <60, rapidly declining, or uncertain cause. Avoid nephrotoxins (NSAIDs)

Optimize Heart Failure (if High Ratio with CHF)

Heart failure reduces kidney perfusion, causing pre-renal azotemia with elevated ratio:

• Diuretic optimization: Loop diuretics (furosemide) reduce congestion and improve kidney perfusion. May temporarily worsen ratio but improves long-term
• ACE inhibitors/ARBs: Improve cardiac output and kidney perfusion. A small initial creatinine rise is expected
• SGLT2 inhibitors: Empagliflozin, dapagliflozin improve heart failure outcomes and kidney function
• Monitor closely: Check BUN, creatinine, electrolytes frequently when adjusting diuretics. Watch for over-diuresis (worsening ratio)
• Avoid nephrotoxins: NSAIDs worsen heart failure and kidney function. Use acetaminophen for pain

Address Low Ratio (<10)

Low BUN/creatinine ratio indicates reduced urea production relative to creatinine:

• Liver disease: Cirrhosis reduces urea synthesis. Check ALT, AST, bilirubin, albumin, PT/INR. Treat underlying liver disease
• Malnutrition: Inadequate protein causes low BUN. Increase protein to 1.0-1.5 g/kg daily. Nutritional supplementation if needed
• SIADH: Syndrome of inappropriate ADH causes dilutional hyponatremia and low BUN. Fluid restriction, treat underlying cause
• Pregnancy: Normal dilutional effect—low BUN with increased GFR. No treatment needed
• Overhydration: Excessive IV fluids or compulsive water drinking. Restrict fluids appropriately