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Creatinine Test
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Creatinine Test

A creatinine test measures levels of a waste product in your blood or urine to help evaluate how well your kidneys are functioning.

What is a creatinine test?

Creatinine is a normal waste product produced when muscle tissue breaks down. Healthy kidneys filter creatinine from the blood and remove it through urine. If kidney function is impaired, creatinine can build up in the blood. This test may be performed on blood or urine, sometimes as part of a comprehensive metabolic panel (CMP) or basic metabolic panel (BMP).

What is it used for?

The test helps check kidney health, diagnose kidney disease, monitor existing kidney problems, and check for medication side effects. Because creatinine levels vary based on muscle mass, age, and activity, results are often used in calculations:

  • eGFR (estimated glomerular filtration rate): A calculation based on blood creatinine, age, weight, height, and sex to estimate how well kidneys filter waste.
  • Creatinine clearance: Compares blood and urine levels to estimate filtration speed.
  • Urine albumin to creatinine ratio (UACR): Compares albumin and creatinine in urine to detect kidney damage.

Why do I need a creatinine test?

You may need this test for a routine checkup, if you have symptoms of kidney disease (such as swelling, fatigue, or changes in urination), or if you are at high risk. Risk factors include diabetes, high blood pressure, heart disease, obesity, smoking, being over 50, or a family history of kidney issues.

What happens during the test?

  • Blood test: A sample is drawn from a vein in your arm.
  • Urine test: You may be asked to collect all urine passed over 24 hours. This involves starting with an empty bladder, collecting all subsequent urine in a provided container (kept refrigerated or on ice), and finishing with a final collection exactly 24 hours later.

Preparation and Risks

You may be asked to avoid eating meat for 24 hours before the test, as it can temporarily increase creatinine levels. If the test is part of a CMP or BMP, you may need to fast for up to 12 hours. Always inform your provider of all medications and supplements you are taking. Risks are minimal, limited to slight pain or bruising at the blood draw site.

What do the results mean?

Normal results depend on your individual muscle mass and lifestyle. A normal result does not always rule out early-stage kidney disease, as levels may remain stable until damage becomes more serious. High blood creatinine may indicate kidney injury, dehydration, or muscle disorders, while low levels may be linked to malnutrition or severe liver disease.

Frequently Asked Questions

Because creatinine is a breakdown product of muscle, people with greater muscle mass naturally have higher baseline levels. In such cases, eGFR equations that include race and sex may underestimate kidney function. Your clinician might use cystatin C‑based eGFR or focus on trends rather than a single value to assess kidney health.
void high‑protein meals (especially meat) for the 24‑hour collection period, as they can artificially raise urinary creatinine. Discontinue supplements that contain creatine (e.g., creatine monohydrate) at least 48 hours prior. Inform the lab about any diuretics, NSAIDs, or ACE inhibitors, as they can affect clearance; your provider may advise temporary cessation, but only under medical supervision.
UACR is more sensitive for early kidney damage, especially in diabetes or hypertension, because it detects small amounts of albumin leaking into urine before creatinine rises. It’s the test of choice for annual screening in patients with diabetes, chronic hypertension, or a family history of kidney disease, even when blood creatinine appears normal.
Creatinine alone can be influenced by muscle mass, diet, and hydration. A modest rise with a normal eGFR (≥ 90 mL/min/1.73 m²) usually indicates that overall filtration is still adequate. Your doctor will likely monitor trends over time and may repeat the test in 3–6 months, especially if you have risk factors like diabetes or hypertension.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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