Creatinine – Understanding Your Blood Test Result

Section Editor: Christopher McCudden Ph.D., DABCC, FADLM, FCACB
September 13, 2026

Creatinine is a waste product that your muscles make every day. Your kidneys filter it out of your blood and remove it in your urine. Because healthy kidneys clear creatinine at a steady rate, the amount left in your blood is one of the most useful signs of how well your kidneys are working. A creatinine test is one of the most commonly ordered blood tests. It appears on a basic metabolic panel, on a comprehensive metabolic panel, and on most routine check-ups.

This article explains what creatinine measures, what a high or low result can mean, and the common reasons a result can change without kidney disease being the cause.

The reference range that applies to your result is the one printed on your laboratory report, not the typical ranges shown here. Reference ranges vary between laboratories based on the equipment used, the population tested, and individual factors such as age, sex, and pregnancy status. Always compare your result to the reference range printed on your own report, and discuss any abnormal result with your doctor.

What does the creatinine test measure?

Creatinine comes from creatine, a substance your muscles use to make energy. As muscles work, a small and fairly constant amount of creatine breaks down into creatinine. That creatinine travels in your blood to your kidneys.

Your kidneys contain about a million tiny filters called nephrons. Nephrons remove waste products from your blood and pass them into your urine. Creatinine is filtered out almost entirely, and very little is reabsorbed. That is what makes it so useful. If your kidneys slow down, creatinine builds up in your blood and the level rises.

A typical adult blood creatinine level is about 0.6 to 1.2 mg/dL (53 to 106 µmol/L) for men and about 0.5 to 1.0 mg/dL (44 to 88 µmol/L) for women. Men usually have higher levels than women because they generally carry more muscle. Exact ranges vary between laboratories.

What is eGFR, and why does it appear next to creatinine?

Most reports show a second number beside creatinine called the estimated glomerular filtration rate, or eGFR. This is not a separate test. It is a calculation that takes your creatinine result and adjusts it for your age and sex, and sometimes your body size.

The eGFR estimates how much blood your kidneys filter each minute. It is reported in mL/min/1.73m². A result of approximately 90 or above is generally considered normal kidney function. A result below 60 that persists for three months or more is one way doctors define chronic kidney disease. Because eGFR is calculated from creatinine, anything that changes your creatinine also changes your eGFR.

How is the creatinine test performed?

Creatinine is measured on a small sample of blood, usually taken from a vein in your arm. You don’t need to fast for a creatinine test on its own. If creatinine is ordered as part of a larger panel, you may be asked to fast for the other tests in that panel.

Your doctor may also order a urine creatinine test. This measures creatinine in a urine sample rather than in blood, and it is used differently. Urine creatinine is often used to correct other urine measurements, such as the protein-to-creatinine ratio, which checks for protein leaking into the urine.

What do creatinine results mean?

Your report may show creatinine in mg/dL or in µmol/L, printed next to a reference range. The units depend on where you were tested. Read a creatinine result alongside your eGFR, other kidney tests, and previous results. A single value rarely tells the whole story.

A normal creatinine level — a result inside the reference range suggests your kidneys are filtering waste as expected. It does not rule out every kidney problem. Some kidney conditions show up first as protein in the urine while creatinine is still normal.
A high creatinine level — a result above the reference range on your report means creatinine is building up in your blood. The most common explanation is that your kidneys are filtering more slowly than usual. This can be temporary or long-standing. A mildly high result in someone who is well is often repeated before any further action is taken.
A low creatinine level — a result below the reference range is usually not a concern. It most often reflects lower muscle mass rather than an organ problem. It can also occur in pregnancy, which is expected.
A rising creatinine level over time matters more than any single value. Your doctor compares your result to earlier ones. A creatinine that has climbed steadily across several tests is followed more closely than one that has been stable for years, even if both are outside the range.

Creatinine is a late signal. The kidneys have a large reserve, so creatinine often stays within the normal range until kidney function has already fallen substantially. This is one reason doctors order other tests alongside it.

What conditions and factors can affect creatinine?

Many things change a creatinine result, and most of them are not kidney disease. That’s why doctors usually repeat a single high value rather than act on it.

Common reasons creatinine can be high

Dehydration — less fluid in the blood concentrates everything in it, including creatinine. This is one of the most common reasons for a temporary rise.
A large amount of muscle — more muscle produces more creatinine. Bodybuilders and very muscular people often run above the standard range even when their kidneys are healthy.
Intense exercise shortly before the test — a hard workout can raise creatinine for a day or two.
A high-protein meal, especially cooked meat — this can raise the result modestly for several hours.
Creatine supplements — these are a direct source of creatinine and commonly raise the level.
Some medicines — certain drugs block creatinine from being secreted into the urine without changing kidney filtration at all. Others can affect the kidneys themselves. Do not stop any medicine because of a blood test. Ask the doctor who prescribed it.
Reduced blood flow to the kidneys — this can happen with severe infection, heart failure, or a sudden drop in blood pressure.
A blockage below the kidneys — such as a kidney stone or an enlarged prostate that stops urine draining freely.
Chronic kidney disease — long-standing damage to the nephrons, most often from diabetes or high blood pressure.

Common reasons creatinine can be low

Less muscle than average — this is the usual explanation. It is common in older adults, in underweight people, and in anyone unwell or immobile for a long time.
Pregnancy — blood volume increases, and the kidneys filter faster, so creatinine normally falls.
Severe liver disease — the liver is involved in making creatinine, so advanced liver disease can lower creatinine.

Because muscle mass affects the result so strongly, creatinine can be misleading at both extremes. A very muscular person may look as though their kidneys are struggling when they are not. An older adult with little muscle may have a creatinine inside the normal range while their kidney function is genuinely reduced. This is one reason eGFR is reported alongside it, and why doctors sometimes add other tests.

What other tests are ordered with creatinine?

Creatinine is rarely interpreted alone. Your doctor usually looks at it together with several other results.

Urea, also called blood urea nitrogen or BUN — another waste product cleared by the kidneys. The relationship between urea and creatinine helps show whether a rise is caused by dehydration or by the kidneys themselves.
Electrolytes — sodium, potassium, chloride, and bicarbonate. Kidneys that aren’t filtering well often disrupt these.
Urine protein or albumin — protein leaking into the urine is often the earliest sign of kidney damage, sometimes appearing while creatinine is still normal.
Cystatin C — another blood marker of kidney filtration that is not affected by muscle mass. It is sometimes used when creatinine is thought to be misleading.

What happens after a creatinine test?

What happens next depends on the result, on your previous results, and on how you are feeling.

A single mildly abnormal creatinine in someone who is well is very often repeated, sometimes after making sure you are well hydrated. Many results return to normal on the second test. If the result stays high, your doctor may order urine testing, a kidney ultrasound, or a referral to a kidney specialist called a nephrologist. If creatinine rises quickly, your doctor will look for a reversible cause, such as dehydration, a new medicine, or a blockage.

If your creatinine has been stable for years at a level slightly outside the printed range, that pattern is usually reassuring rather than alarming. Your own trend is the most useful comparison you have.

Questions to ask your doctor

What was my creatinine level, and what is my eGFR?
How does this result compare with my previous results?
Could anything else explain this result, such as dehydration, exercise, or a medicine I take?
Do you want to repeat the test, and if so, when?
Should I have my urine checked for protein?
Do any of my current medicines need to be reviewed because of this result?
Is there anything I should do differently before my next blood test?
When would you refer me to a kidney specialist?