In short
- A high BUN or urea most often means dehydration, a lot of protein in your diet, or reduced kidney function. The pattern with creatinine helps tell these apart.
- European reports give urea in mmol/L; US reports give BUN in mg/dL. Multiply urea in mmol/L by 2.8 to get BUN in mg/dL.
- Our reference range is urea 2.8–7.5 mmol/L, which is a BUN of about 7.8–21 mg/dL.
- Urea up with normal creatinine points away from the kidneys: fluid loss, protein, corticosteroids or bleeding high in the gut. Both up points more toward the kidneys.
- For kidney function itself, eGFR is more reliable than urea.
- Low urea is usually harmless and follows a low-protein diet, pregnancy or, less often, liver disease.
Urea is one of the oldest kidney tests, and one of the most misread. A high value can mean your kidneys struggle, or simply that you drank too little the day before. This guide shows how to tell the difference with creatinine, eGFR and the BUN-to-creatinine ratio.
What does a high BUN or urea mean?
A high BUN or urea means more urea nitrogen is in your blood than usual, which can come from reduced kidney function but also from dehydration or a high-protein diet. Urea is a waste product that forms when your body breaks down protein. The kidneys remove it in urine.
Because urea depends on the kidneys, on hydration and on protein intake, it is less specific than creatinine. MedlinePlus lists dehydration, burns, certain medicines, a high-protein diet and a recent heart attack as reasons for a higher level. It also notes that BUN varies by sex and usually increases with age.
StatPearls adds causes outside the kidneys: bleeding in the upper digestive tract, states where the body breaks down a lot of tissue, and oral corticosteroids. So one high urea on its own does not mean kidney disease.
Urea or BUN: which number is on my report?
Urea and BUN measure the same substance in different units. European labs, including Slovenian ones, usually report urea in mmol/L. US labs report blood urea nitrogen (BUN) in mg/dL, which counts only the nitrogen part of urea.
- Urea (mmol/L) × 2.8 = BUN (mg/dL).
- BUN (mg/dL) ÷ 2.8 = urea (mmol/L).
- Creatinine (µmol/L) ÷ 88.4 = creatinine (mg/dL).
Some reports give "urea" in mg/dL. That number is about 2.14 times the BUN, so check the label and unit before you compare. Mixing these up is one of the most common reading errors we see with kidney values.
What is the normal range for urea and BUN?
Blood Lab 360 treats urea from 2.8 to 7.5 mmol/L as within range, which equals a BUN of about 7.8 to 21 mg/dL. Values above that are raised, and values below are low. Creatinine and eGFR from the same report give the kidney context.
| Marker | Value | How Blood Lab 360 reads it |
|---|---|---|
| Urea | Below 2.8 mmol/L (BUN below 7.8 mg/dL) | Low. Read in context: diet or liver. |
| Urea | 2.8–7.5 mmol/L (BUN 7.8–21 mg/dL) | Within the reference range. |
| Urea | Above 7.5 mmol/L (BUN above 21 mg/dL) | Raised. Hydration or kidneys; seek advice if it persists. |
| Creatinine | Up to 100 µmol/L (1.13 mg/dL) | Within the reference range. |
| Creatinine | 100–120 µmol/L (1.13–1.36 mg/dL) | Slightly raised. Look at eGFR. |
| Creatinine | Above 120 µmol/L (1.36 mg/dL) | Raised. Read with eGFR and see a doctor. |
| eGFR | 90 or more; 60–89; below 60 mL/min/1.73 m² | Normal; mildly reduced; reduced. |
Source: urea and creatinine follow the Nordic Reference Interval Project (NORIP, Rustad et al., 2004); eGFR categories follow KDIGO 2024. Reference ranges differ between laboratories, and creatinine limits often differ for men and women.
What does the BUN/creatinine ratio mean?
The BUN/creatinine ratio compares two waste products to hint at why urea is raised. StatPearls gives three rough patterns. When the problem lies before the kidneys, such as dehydration, the ratio is close to 20:1. In disease of the kidney itself, it is closer to 10:1. Bleeding in the upper digestive tract can push it very high, sometimes above 30:1.
The ratio uses US units: BUN in mg/dL divided by creatinine in mg/dL. With European units you can estimate it as urea (mmol/L) × 248 ÷ creatinine (µmol/L). For example, urea 10 mmol/L and creatinine 90 µmol/L give a BUN of 28 mg/dL and a creatinine of 1.02 mg/dL. The ratio is about 27:1.
Treat the ratio as a clue, not a diagnosis. MedlinePlus notes that comparing creatinine with BUN from the same test helps find the cause of a kidney problem. It does not replace eGFR, a urine test or a doctor's exam.
Patterns: urea with creatinine, eGFR and albumin
Urea says most when you read it with the other markers from the same report. These are the combinations Blood Lab 360 looks at:
- Urea raised, creatinine and eGFR normal. Common after too little fluid, a high-protein diet or corticosteroids. Repeat after a normal day of drinking and eating.
- Urea raised, sodium raised, albumin above 48 g/L (4.8 g/dL). This fits dehydration. A mildly high albumin is most often due to dehydration or a long tourniquet at the draw.
- Urea raised, ratio above 30:1, creatinine normal, haemoglobin low. Think of bleeding high in the digestive tract. This needs a doctor promptly, not a repeat in weeks.
- Urea and creatinine both raised, eGFR below 60. Kidney function is reduced. Kidney function changes slowly, so confirm it after about 2–4 weeks. KDIGO defines chronic kidney disease by eGFR below 60 lasting more than three months. See eGFR and creatinine.
- Urea low, albumin below 36 g/L (3.6 g/dL). Low protein intake, or less often liver disease. StatPearls lists starvation, a low-protein diet and severe liver disease as causes of low urea.
- Urea low, everything else normal. Usually harmless: a plant-based or low-protein diet, or pregnancy.
If urea is high together with abnormal potassium or sodium, read our potassium and sodium guide as well. Dehydration often moves sodium and urea together.
What does a low BUN mean?
A low BUN or urea is usually not a health problem and most often reflects low protein intake. MedlinePlus lists a lack of protein in the diet, malnutrition and liver disease. Our knowledge base adds pregnancy. It matters mainly when albumin is also low or liver tests are abnormal.
Can food, fluids or a blood test day change urea?
Yes, urea responds to what you did in the day or two before the test. Too little fluid and a large protein load both raise it. MedlinePlus says no special preparation is usually needed for BUN, but fasting may apply if other tests are done at the same draw.
For a fair reading, drink normally and eat as usual the day before. Our blood test preparation guide explains why a large meat meal or creatine the day before can make kidney values look worse. One raised urea after a hot day with little water is rarely an emergency. A steady rise over several tests, with creatinine climbing too, is the pattern that matters.
See a doctor quickly if raised urea comes with black, tarry stools or vomiting blood, or with dizziness or fainting. These can be signs of bleeding in the gut. The same applies if urea and creatinine both rise and you pass much less urine, have new swelling in the legs, or feel very unwell. An eGFR below 60 for the first time needs a GP review within weeks, not months.
How Blood Lab 360 reads this
Blood Lab 360 reads urea against the NORIP reference interval. Urea is not a KDIGO staging marker, so the app does not stage kidney disease from it. It shows urea next to creatinine, eGFR, albumin, sodium and haemoglobin from the same report. It explains when a pattern fits dehydration better than kidney disease.
For kidney assessment, the app treats eGFR as the more reliable marker and urea as context about hydration and protein. It suggests confirming an abnormal result after about 2–4 weeks and following kidney markers over 3–6 months. For a stable value, the re-test interval is about 24 weeks. It does not give a diagnosis. For values just outside the range, see what an out-of-range result means.
Frequently asked questions
What does an elevated BUN mean?
More urea nitrogen in the blood than usual. The most common reasons are dehydration, a high-protein diet or reduced kidney function. Creatinine and eGFR from the same test help show which one applies.
Can dehydration raise BUN?
Yes. Dehydration is one of the most common reasons for a high BUN. Urea often rises more than creatinine, so the ratio goes up. Repeat the test after a normal day of drinking.
What is a normal BUN/creatinine ratio?
StatPearls describes a ratio near 20:1 when the cause lies before the kidneys, such as dehydration, and near 10:1 in kidney disease itself. Above 30:1 can occur with bleeding high in the gut.
What does a low BUN mean?
Usually low protein intake, and it is rarely a concern. Malnutrition, pregnancy and liver disease are other causes. It matters more if albumin is also low.
Does eating a lot of protein raise urea?
Yes. A high-protein diet raises urea because urea comes from protein breakdown. Eat normally the day before a kidney test so the result reflects your usual state.
Is a high urea a sign of kidney failure?
Not on its own. Kidney disease is judged mainly by eGFR, creatinine and urine tests over time. Urea together with a low eGFR points to the kidneys; urea alone often reflects hydration.
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- MedlinePlus (NIH): BUN (Blood Urea Nitrogen) (2024)
- MedlinePlus (NIH): Creatinine Test (2024)
- KDIGO: 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease (2024)
- StatPearls (NCBI Bookshelf): Renal Function Tests (2024)
- MedlinePlus (NIH): Gastrointestinal bleeding (2024)
Links checked on 14 Sep 2026. The marker ranges above carry their own source next to each row.
Related
What do eGFR and creatinine mean? How kidney function is assessed, when a value is worrying and how to protect your kidneys naturally.
Blood chemistry panel normal values for ALT, AST, GGT, CK, creatinine and glucose, each with a source, plus what S- means on a lab report and µkat/L to U/L.
Albumin low or high on your blood test? Normal range in g/L and g/dL, causes of low albumin, why it changes slowly, and which patterns need a doctor.
This article is for information only and is not a substitute for medical advice. Talk to your doctor about your results.