What is BUN creatinine ratio?
The BUN creatinine ratio is blood urea nitrogen ÷ serum creatinine (same units, usually mg/dL). A normal BUN creatinine ratio range is typically 10–20. Above 20 often suggests prerenal azotemia (for example dehydration); below 10 can suggest intrinsic renal injury or low urea generation.
What is the BUN creatinine ratio?
Blood urea nitrogen (BUN) and creatinine are both filtered by the kidneys, but they behave differently along the nephron. Creatinine is filtered and mostly excreted; urea nitrogen is filtered and partially reabsorbed. That difference is why the bun creatinine ratio kidney function signal is useful: when filtration slows and tubular flow falls, urea reabsorption rises relative to creatinine, and the ratio climbs.
Clinicians use this bun creatinine test calculator online style ratio as a quick bedside clue — not a replacement for eGFR, creatinine clearance, urine studies, or clinical judgment.
How BUN and creatinine move in the kidney
Simplified nephron view: creatinine stays in the tubule; urea can be reabsorbed when flow is low.
Normal BUN to creatinine ratio chart
Visual bands used in this blood urea nitrogen creatinine ratio calculator.
Reference intervals can vary by lab and age — always check local ranges.
BUN creatinine ratio formula
The standard bun creatinine ratio calculation formula is:
- mmol/L BUN
- × 2.8 → mg/dL
- µmol/L creatinine
- ÷ 88.4 → mg/dL
This page is also a bun creatinine ratio mmol/L calculator: choose SI units and the tool converts before dividing. That matches how most bedside and web calculators (including common clinical tools) standardize the ratio.
How to calculate BUN creatinine ratio
- Collect BUN and serum creatinine from the same sample when possible.
- Convert both to mg/dL if your lab reports mmol/L or µmol/L.
- Divide BUN by creatinine — that is the ratio.
- Interpret against the normal range and the patient’s volume status, meds, diet, and acute illness.
Worked example
- Labs: BUN 26 mg/dL, creatinine 0.87 mg/dL.
- Divide:
26 ÷ 0.87 = 29.9. - Meaning: Ratio > 20 → consider bun creatinine ratio prerenal azotemia causes such as dehydration.
Normal BUN creatinine ratio range
Most educational and clinical references cite a normal bun creatinine ratio range of roughly 10 to 20. Individual labs may publish slightly different cutoffs. Age, protein intake, muscle mass, and liver function all shift absolute BUN and creatinine — so the ratio must be read with context.
| Ratio | Category | Typical clinical clue |
|---|---|---|
| < 10 | Low | Intrinsic renal injury, low urea generation, SIADH, pregnancy |
| 10 – 20 | Normal | Usual adult reference band |
| > 20 | High | Prerenal azotemia, dehydration, GI bleed, high protein load |
BUN creatinine ratio interpretation
What does elevated bun creatinine ratio mean? In many patients it means the kidneys are under-perfused or urea production/reabsorption is relatively high compared with creatinine. That is why a bun creatinine ratio dehydration story is so common — volume loss lowers GFR and increases urea reabsorption.
BUN creatinine ratio 20 meaning: twenty is the classic upper border of “normal.” Mildly above 20 (for example 21–25) should still prompt a look at fluids, heart failure, GI bleeding, and diet — especially if creatinine is also rising.
High BUN creatinine ratio causes
- Dehydration / hypovolemia
- Shock, burns, heart failure
- Gastrointestinal bleeding
- High protein intake
- Advanced age
- Corticosteroids / Cushing physiology
Low BUN creatinine ratio causes
- Acute tubular necrosis
- Liver disease / malnutrition
- Pregnancy
- SIADH
- Rhabdomyolysis (creatinine surge)
BUN creatinine ratio calculator pediatric notes
The arithmetic for a bun creatinine ratio calculator pediatric case is the same (BUN ÷ creatinine). Reference interpretation, however, can differ in neonates and infants because urea generation, diet, and muscle mass change rapidly. Prefer age-specific lab references and pediatric nephrology guidance rather than adult cutoffs alone.
FAQ
What is BUN creatinine ratio?
The BUN creatinine ratio is blood urea nitrogen divided by serum creatinine (usually both in mg/dL). It is a quick bedside clue for kidney function patterns, especially prerenal vs intrinsic azotemia.
How do I use this BUN creatinine ratio calculator?
Enter BUN and creatinine, choose mg/dL or SI units, then tap Calculate. This bun creatinine test calculator online converts units, divides the values, and shows low / normal / high interpretation.
What is the BUN creatinine ratio formula?
BUN creatinine ratio formula: BUN (mg/dL) ÷ serum creatinine (mg/dL). For mmol/L BUN multiply by 2.8 first; for µmol/L creatinine divide by 88.4 first.
How to calculate BUN creatinine ratio step by step?
1) Get BUN and creatinine from the same draw. 2) Convert both to mg/dL if needed. 3) Divide BUN by creatinine. 4) Compare with the normal bun creatinine ratio range of about 10–20.
What is a normal BUN creatinine ratio range?
Most references use about 10–20 as the normal BUN to creatinine ratio chart band for adults. Lab-specific intervals can differ slightly.
What does a BUN creatinine ratio of 20 mean?
A ratio of 20 is at the upper edge of the usual normal range. It can still be acceptable, but if the patient looks volume depleted, review for early prerenal azotemia or dehydration.
What does an elevated BUN creatinine ratio mean?
An elevated ratio (typically >20) often means relatively more urea retention/reabsorption than creatinine — classic for bun creatinine ratio prerenal azotemia, dehydration, hypovolemia, heart failure, GI bleeding, or high protein load.
What are high BUN creatinine ratio causes?
Common high BUN creatinine ratio causes include dehydration, hypovolemia, shock, congestive heart failure, gastrointestinal bleeding, high protein intake, advanced age, and corticosteroid effect.
What are low BUN creatinine ratio causes?
Low BUN creatinine ratio causes (<10) include acute tubular necrosis, liver disease, malnutrition, pregnancy, SIADH, and rhabdomyolysis (creatinine rises disproportionately).
Can this work as a BUN creatinine ratio mmol/L calculator?
Yes. Choose mmol/L for BUN and/or µmol/L for creatinine. The calculator converts to mg/dL before applying the bun creatinine ratio calculation formula.
Is there a BUN creatinine ratio calculator pediatric difference?
The math is the same, but pediatric reference interpretation can differ—especially in neonates and infants. Prefer age-specific lab ranges rather than adult 10–20 cutoffs alone.
Is this the same as a creatinine clearance or kidney function calculator?
No. This blood urea nitrogen creatinine ratio calculator helps localize azotemia. Creatinine clearance estimates GFR for dosing. Use our creatinine clearance calculator when you need Cockcroft-Gault CrCl.
Educational use only. This calculator does not diagnose disease or replace clinician judgment. Estimating ratios are approximations — interpret with the full clinical picture.