Creatinine test explained

What the test measures

Creatinine is a waste product made when muscles use creatine, a compound that stores energy. Your muscles release creatinine into the blood at a fairly steady rate each day. Healthy kidneys filter it out of the blood and pass it into the urine.

When the kidneys filter less well, creatinine builds up and the blood level rises. That is why the test is used as a marker of kidney filtration. The test on your report may be called serum creatinine (serum is the liquid part of blood after it clots) or plasma creatinine.

One important limit: creatinine often stays within the lab's reference range until a large part of kidney filtration has been lost. A "normal" creatinine does not always mean normal kidneys, and a slightly raised one does not always mean kidney disease.

Why it is ordered

Creatinine is one of the most common blood tests in Kenya. It is often part of a routine panel that labs call "UECs" (urea, electrolytes and creatinine), "RFTs" or "kidney function tests". A clinician may request it:

• as a check for people with diabetes, high blood pressure (presha), heart disease or a family history of kidney disease
• before starting, or while taking, medicines that are cleared by the kidneys or can affect them
• to investigate symptoms such as swollen feet, tiredness or changes in urination
• before a scan that uses contrast dye, or before surgery
• during a hospital admission, to watch for sudden changes in kidney function
• to follow up known chronic kidney disease (CKD) over time

How the sample is taken and how to prepare

A small amount of blood is taken from a vein in your arm. It takes a few minutes, and many labs in Mombasa give results the same day.

Preparation is usually simple. If your clinician or lab advises it:

• Avoid a large meal of cooked meat in the 12 hours before the test. Cooking turns some of the creatine in meat into creatinine, which can raise the blood level for several hours. Nyama choma the night before is a common example.
• Avoid heavy exercise the day before and on the morning of the test, as hard muscle work can raise creatinine for a short time.
• Tell the lab and your clinician about supplements, especially creatine used for gym training, and about any medicines you take.
• Drink normally unless told otherwise. Being very dehydrated can raise the result.

You do not normally need to fast for creatinine alone. If other tests on the same form need fasting, follow those instructions.

How results are reported

Most Kenyan labs report creatinine in micromoles per litre (µmol/L). Some labs, and some reports from outside Kenya, use milligrams per decilitre (mg/dL). The two units describe the same thing:

For example, 1.0 mg/dL is about 88 µmol/L. Always check which unit is printed, especially when comparing reports from two different labs.

Reference ranges vary. This page does not give a fixed "normal" number, because the range depends on the lab's method, your age, your sex and your muscle mass. Use the reference range printed on your own report. A result flagged "H" (high) or "L" (low) is outside that lab's range, which is a prompt for discussion, not a diagnosis.

Many labs now also print an eGFR next to the creatinine. The eGFR is usually more useful to read than the creatinine number itself.

What can affect the result

Creatinine reflects muscle as well as kidneys, so several things change it without any change in kidney filtration:

• Muscle mass. Very muscular people tend to have higher creatinine. Older adults, people who are very thin, and people who have lost muscle through illness or amputation tend to have lower creatinine, which can hide reduced kidney function.
• Diet. A recent meal of cooked meat can raise the level for several hours. A mostly plant-based diet tends to give slightly lower levels.
• Hydration. Dehydration, from vomiting, diarrhoea, heat or not drinking enough, can raise creatinine, and it often improves once fluid is replaced.
• Medicines. Some medicines reduce how much creatinine the kidney tubules release into the urine. The blood level rises slightly even though filtration has not changed. Other medicines can genuinely affect the kidneys. Your clinician can tell which applies.
• Pregnancy. Filtration increases in pregnancy, so creatinine is normally lower. A value that looks ordinary may be relatively high for a pregnant woman.
• Lab method. Labs use either a chemical method (often called Jaffe) or an enzymatic method. High blood sugar with ketones, high bilirubin and some medicines can interfere with the chemical method. Differences between labs are one reason to repeat a surprising result at the same lab where possible.

What creatinine cannot tell you on its own

A creatinine result alone cannot confirm or rule out chronic kidney disease. International guidance from KDIGO (Kidney Disease: Improving Global Outcomes, 2024) says kidney function should be estimated as an eGFR using a validated equation, and that CKD is assessed with eGFR and urine albumin (measured as urine ACR) together. CKD also requires the changes to be present for more than 3 months.

Creatinine does not tell you:

• the cause of any kidney problem
• whether protein is leaking into the urine, which can happen even when creatinine is in range
• whether a change is sudden (acute) or long-standing, unless earlier results are available to compare

This is why keeping your old results matters. Many people in Mombasa receive results from a lab or a hospital outpatient clinic and carry the paper to their doctor. Bring every earlier report you have, even from a different lab.

Related tests

• eGFR: estimated filtration, calculated from creatinine, age and sex.
• Urine ACR: checks for albumin leaking into the urine.
• Kidney function tests: the wider panel with urea and electrolytes.
• Urinalysis: a general urine test for blood, protein and infection.

When to discuss your result with a clinician

Book a review with a doctor or clinical officer if:

• your creatinine is flagged high, or your eGFR is below 60
• your result has risen compared with an earlier test
• you have diabetes or high blood pressure and have not had a urine ACR test
• you have swelling, foamy urine or changes in how much you pass urine

If you are not sure where to start, our page on what to do after a high creatinine result walks through the next steps.

Common questions

Do I need to fast for a creatinine test?

Fasting is not usually required for creatinine alone. Some clinicians advise not eating a large meal of cooked meat in the 12 hours before the test. If the same blood sample is used for a fasting sugar or lipid test, you will be told to fast for that reason.

Why was my creatinine repeated?

A single raised result can be affected by dehydration, a recent illness, a meat meal, exercise or a medicine. Repeating the test shows whether the result is stable, rising or back to your usual level. Change over time tells a clinician much more than one value.

This page explains what a test or condition involves. It is not a diagnosis and does not replace advice from a doctor who knows your history. Your results should be interpreted together with your symptoms, other tests and a clinical assessment. Medical disclaimer.