BUN/Creatinine Ratio
The ratio of blood urea nitrogen (urea) to creatinine helps differentiate pre-renal from intrinsic renal causes of acute kidney injury, and can identify upper GI bleeding.
Score interpretation
Urea:creatinine ratio below 40 (SI units): low protein intake, liver disease, overhydration, intrinsic renal disease (ATN) or SIADH.
→ If AKI present: suspect ATN or intrinsic renal pathology. Check urinalysis, casts. Avoid nephrotoxins. Consider FENa if AKI.
Urea:creatinine ratio 40–100 (SI units): reference range.
→ Normal kidney function or balanced AKI. Interpret in clinical context.
Urea:Creatinine ratio > 100: Suggests pre-renal azotaemia (dehydration, heart failure, sepsis) or upper GI haemorrhage (urea absorbed from digested blood).
→ Pre-renal: IV fluid challenge; reassess urea after rehydration. Upper GI bleed: check for haematemesis/melaena; urgent gastroscopy. Cardiac: treat HF. Avoid NSAIDs/contrast.
Interpretation bands for the BUN/Cr Ratio. Apply clinical judgement and local guidance.
References
- Higgins C. Urea and creatinine concentration, the urea:creatinine ratio. acutecaretesting.org; October 2016.
Related
Curated clinical cross-links plus same-class fallbacks.
- Emollients, urea-containing · Topical emollient (urea, keratolytic)
- Urea Hydrogen Peroxide Ear Drops · Ear Wax Softening / Cerumenolytic
- Urea hydrogen peroxide · Cerumenolytic
- Carglumic acid · Carbamoyl phosphate synthetase 1 activator (urea cycle defect)
- Urea (13C) · 13C-urea breath test
- Vancomycin (Renal Dosing) · Antibiotic Dosing in CKD
- Hyperkalaemia Management · UK Kidney Association Guidelines 2020; NICE CKD Guidelines
- Rhabdomyolysis · Renal Association 2018; UpToDate 2024
- Hypocalcaemia (Adult) · Society for Endocrinology
- SIADH (Endocrine Perspective) · European Hyponatraemia Guidelines 2014
- Hepatorenal Syndrome · EASL 2018; ICA 2015
- Acute Kidney Injury (AKI) · KDIGO 2012 / NICE AKI 2019
Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.