You were given a referral for a creatinine blood test, and urea also appeared on the form next to it. Let's sort out what these numbers show and why the doctor looks at them together.
What creatinine is and why urea is also checked
Creatinine is the end product of the creatine phosphate reaction. It is formed in the muscles and from there enters the blood. The kidneys remove it in urine. When interpreting the form, look specifically at creatinine.
Urea (BUN, blood urea nitrogen) is measured in the same test panel as creatinine. Creatinine and BUN are compared with each other: this helps determine the cause of a kidney problem.
Why a creatinine and urea blood test is ordered
A creatinine blood test is needed to check how the kidneys are working. It is also ordered when there are symptoms that resemble kidney problems.
Creatinine is part of the basic and comprehensive metabolic panel. These are sets of routine biochemical tests. That is how the urea test comes together with other indicators.
The third purpose is monitoring an already known disease. The numbers show how treatment is progressing. A separate reason is monitoring the side effects of medications that affect the kidneys.
Normal creatinine: what the values depend on
The creatinine level in the blood depends on the amount of muscle mass. In men the normal range is higher than in women.
- Women: 44.0–80.0 µmol/L
- Men: 74.0–110.0 µmol/L
- Children under 1 year: 18–35 µmol/L
- Children from 1 to 14 years: 27–62 µmol/L
Daily urinary excretion: in men 8.8–17.7 mmol, in women 7.1–15.9 mmol. This is clearance, that is, the amount per day.
Muscles do not change quickly. Therefore the creatinine level in the blood is fairly constant. In a person with a large muscle mass, the number may be above normal without disease.
Why creatinine and urea may deviate from normal
High creatinine in the blood alone occurs in kidney failure. If it is elevated both in the blood and in the urine, the cause is often a heavy meat diet.
Creatinine levels rise with dehydration, muscle damage, and physical exertion. Low levels occur with a vegetarian diet, fasting, and in the first and second trimesters of pregnancy.
Chronic kidney disease is usually caused by other conditions. These are high blood pressure, diabetes, high cholesterol, kidney infections, glomerulonephritis. Also hereditary polycystic disease, stones, and an enlarged prostate that obstructs urine flow. Long-term use of lithium or nonsteroidal anti-inflammatory drugs also has an effect.
Creatinine has a weak point. It may remain normal even when the glomerular filtration rate falls by 50%. Therefore one indicator is not enough. There is a more sensitive marker — cystatin C.
How the test is done and what is considered when interpreting it
Blood is drawn from a vein in the arm with a thin needle. The whole thing takes less than five minutes. A small bruise or a sensation from the needle remains.
Preparation depends on the purpose. Sometimes you are asked not to eat meat for 24 hours before the test. For the panel, fasting for up to 12 hours may be required. Tell the doctor about medications and supplements in advance, but do not stop them yourself.
When interpreting, the estimated glomerular filtration rate, eGFR, is calculated from creatinine. The formula includes age, weight, height, and sex. This indicator is more accurate than the creatinine number itself and shows the severity of the disease. Blood creatinine is also compared with urine creatinine — this is clearance. And the urine albumin-to-creatinine ratio, UACR, shows protein leakage.
When to see a doctor with the results
The doctor evaluates a result outside the normal range together with symptoms and other tests. The doctor, not a search engine, decides on the approach.
You should also pay attention to symptoms. These are swelling of the hands, feet, or eyelids, dry skin, itching, numbness. Fatigue, loss of appetite and weight, muscle cramps. Nausea, vomiting, shortness of breath, problems with sleep and with clarity of thinking. The volume of urine changes, and blood or foam appears in it.
Early stages of kidney disease often occur without symptoms. The problem is found by chance, through a test done for another reason. People at risk include those with diabetes, hypertension, heart disease, smokers, people with obesity, those over 50, and those with a family history. They may be advised to have regular check-ups.
A creatinine deviation on its own is not a reason to call an ambulance; 103/112 — for signs of a life-threatening condition, such as a stroke or heart attack.
The text is for reference. It does not replace a doctor's consultation: the doctor reviews the form and the history as a whole.
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This content is for reference and does not replace a doctor's consultation. Medical disclaimer