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Kidneys and electrolytes · Blood
BUN/creatinine ratio
A calculated ratio between urea nitrogen and creatinine; adds little to the individual values.
At a glance
- Measured in blood
- In 1 test panel
- No special preparation
Explanation
BUN/creatinine ratio: what is measured?
The BUN/creatinine ratio is not measured but calculated. The laboratory divides urea nitrogen (BUN, calculated from urea) by creatinine, both in American units (mg/dl). The idea is that urea and creatinine both rise when the kidneys work less well, but that urea rises much more with dehydration, reduced blood flow to the kidneys or increased protein breakdown. The ratio gives a hint as to which of these situations is more likely.
What can it detect?
- A clue to dehydration or reduced blood flow to the kidneys
- A clue to increased protein breakdown, for example due to a protein-rich diet or bleeding in the stomach or intestine
Result
What does the result mean?
BUN/creatinine ratio too high
A high ratio means that urea is relatively more raised than creatinine. This usually fits drinking too little, heavy exercise, a protein-rich diet or protein supplements. Reduced blood flow to the kidneys, for example with heart failure, bleeding in the stomach or intestine, and corticosteroids can also raise the ratio. A high ratio with a normal creatinine and a normal eGFR says little about the kidneys themselves.
BUN/creatinine ratio too low
A low ratio means that urea is relatively low compared with creatinine. This occurs with little protein in the diet, with drinking a lot and with a lot of muscle mass or creatine use, which makes creatinine higher. Rarely, it fits malnutrition or severe liver disease. Usually a low ratio has no significance.
After an abnormal result
An abnormal ratio on its own usually does not lead to separate follow-up. The GP looks at the individual values of urea, creatinine and eGFR and at fluid intake, diet and medicines. If creatinine or eGFR is abnormal, the approach of the Dutch GP guideline (NHG) on chronic kidney disease is followed.
Reliability
How reliable is the test?
The ratio adds little beyond the individual values of urea, creatinine and eGFR. There are no agreed limit values for the ratio. The eGFR and albumin in the urine say more about kidney function; the Dutch GP guideline (NHG) on chronic kidney disease is also based on these. The ratio is mainly reported by American laboratories, in American units. Because both urea and creatinine are affected by diet, fluid and muscle mass, an abnormal ratio in someone without symptoms is hard to interpret.
What can affect the result?
- A protein-rich diet, drinking too little and heavy exercise raise the ratio; a lot of muscle mass and creatine supplements lower it.
- The ratio is calculated in American units and cannot simply be compared with Dutch results.
- A normal ratio does not rule out reduced kidney function, because urea and creatinine then rise together.
Who it is for
Who is the test useful for?
Useful for
The ratio is mainly reported in broad panels that follow the American approach. In people without symptoms, an abnormal ratio says little. If you want your kidney function assessed, creatinine, eGFR and possibly albumin in the urine are more useful.
How common is it?
There are no Dutch figures on how often an abnormal BUN/creatinine ratio occurs, because it is not routinely tested. A slightly abnormal ratio due to diet, fluid or muscle mass occurs regularly in healthy people.
NVKC, allesovertesten.nl; no Dutch registration figure available
Drawbacks and risks
- An abnormal ratio with normal kidney function can cause unnecessary worry or lead to unnecessary further testing.
Get tested
BUN/creatinine ratio: test panels
BUN/creatinine ratio is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.
Evidence
Sources
This explanation is based on Dutch guidelines and independent information. It is general information, not a diagnosis. Discuss an abnormal result with your GP.
More about risks and resultsMore explanations
Other tests: Kidneys and electrolytes
- Chloride
- CO2 (bicarbonate)
- Creatinine
- Creatinine (urine)
- Cystatin C
- eGFR
- Phosphate (inorganic)
- Potassium
- Sodium
- Urea
- Urea nitrogen (BUN)