Acute Kidney Injury with Elevated BUN and Creatinine
This patient has acute kidney injury (AKI) with a BUN of 46 mg/dL and creatinine of 2.81 mg/dL, requiring immediate assessment of volume status, medication review, and determination of pre-renal versus intrinsic renal causes to guide management.
Calculate the BUN/Creatinine Ratio
The BUN/creatinine ratio is 46/2.81 = 16.4:1, which falls within the normal range of 10-15:1 1. This suggests intrinsic renal disease rather than simple pre-renal azotemia, as pre-renal causes typically produce ratios >20:1 2, 3.
Immediate Clinical Assessment Required
Volume Status Evaluation
- Check for jugular venous distension (the most reliable sign of volume overload) 4
- Assess for peripheral edema in legs, presacral area, and abdomen 4
- Measure orthostatic vital signs to detect volume depletion 2, 3
- Review recent body weight changes (most reliable for short-term fluid status) 4
Signs of Hypoperfusion to Assess
- Cool extremities, altered mentation, narrow pulse pressure 4
- Resting tachycardia 4
- The disproportionate elevation of BUN relative to creatinine can indicate reduced cardiac output 4
Determine the Cause
Pre-Renal Causes (Less Likely Given Normal BUN/Cr Ratio)
- Dehydration or volume depletion 2
- Heart failure with reduced cardiac output 2, 3
- Diuretic-induced volume depletion 2
Intrinsic Renal Causes (More Likely)
- Acute tubular necrosis is a common cause with this laboratory pattern 2
- Acute interstitial nephritis (most frequent diagnosis in patients with elevated creatinine and normal urinalysis) 5
- Contrast-induced nephropathy 2
- Diabetic nephropathy or hypertensive nephrosclerosis (if chronic disease present) 2
- Rhabdomyolysis (check creatine kinase if suspected) 6, 7
Post-Renal Causes
- Urinary obstruction (perform bladder scan and renal ultrasound if suspected)
Essential Diagnostic Workup
Laboratory Tests
- Urinalysis with microscopy to rule out intrinsic kidney injury (excellent negative predictive value) 2
- Urine albumin-to-creatinine ratio to assess for proteinuria 2
- Serum electrolytes, particularly potassium (risk of hyperkalemia with this degree of renal dysfunction) 4
- Complete blood count to check for anemia 4
- Creatine kinase if rhabdomyolysis suspected 6, 7
Imaging
- Renal ultrasound to exclude obstruction and assess kidney size
Medication Management
Medications to Review and Potentially Discontinue
- NSAIDs should be stopped immediately as they worsen renal function through decreased perfusion 2, 3
- ACE inhibitors/ARBs: Consider temporary discontinuation in volume depletion, but modest creatinine increases up to 30% or <3 mg/dL are acceptable 2
- Diuretics: Reduce dose if hypovolemia present 3
- Review all nephrotoxic medications 2
Critical Pitfall
Do not discontinue ACE inhibitors/ARBs prematurely—creatinine increases up to 50% above baseline or up to 3 mg/dL are acceptable with these medications 2. However, with creatinine at 2.81 mg/dL, temporary discontinuation may be warranted if volume depletion is present 2, 3.
Estimate Kidney Function
Using the creatinine of 2.81 mg/dL, the estimated GFR is likely 20-30 mL/min/1.73 m², indicating Stage 4 chronic kidney disease if this persists 2. Note that serum creatinine alone is unreliable, as it can be normal even when GFR has decreased by 40% 2.
Management Strategy
If Pre-Renal Component Suspected
- Initiate appropriate fluid repletion if dehydrated 2, 3
- Improvement should occur within 24-48 hours of adequate hydration 2
- If values remain elevated after 48 hours of adequate hydration, intrinsic kidney disease is present 2
If Intrinsic Renal Disease
- Avoid further nephrotoxic insults 2
- Optimize hemodynamics and perfusion 4
- Monitor electrolytes closely, especially potassium 4
Nephrology Referral Indications
Immediate nephrology referral is warranted for 2:
- eGFR <30 mL/min/1.73 m² (which this patient likely has)
- Uncertainty about etiology of kidney disease
- Rapidly progressing kidney disease
- Difficult management issues
Prognostic Considerations
This degree of renal dysfunction carries significant mortality risk. Baseline BUN and creatinine are strong predictors of in-hospital mortality 4. Worsening renal function during hospitalization is associated with increased mortality (OR 2.7,95% CI 1.6-4.6) 4. Higher BUN levels independently predict adverse renal outcomes and progression to end-stage renal disease 8.