Serum Creatinine (with optional 24-hour urine collection for creatinine clearance calculation)

This test measures the amount of creatinine in your blood, which shows how well your kidneys are filtering waste from your body. Because kidney disease often causes no symptoms in its early stages, this simple blood test can help your doctor find a problem early, when treatment works best.

Creatinine is a byproduct of muscle metabolism and is naturally filtered out of your blood by your kidneys. High levels can indicate kidney problems, while low levels might suggest dehydration or muscle loss. This test is often used alongside other kidney function tests to monitor overall kidney health.

For a basic creatinine blood test, you can usually eat and drink normally, and no special preparation is needed. Let your doctor know about all prescription medicines, over-the-counter drugs, and supplements you take, since some of them can affect your results. During the test, a member of the care team will draw a small blood sample from a vein in your arm, which takes only a few minutes.

For a blood test, you’ll typically have a small needle inserted into your arm to draw blood. For a 24-hour urine test, you’ll collect all urine over a full day in a special container. Avoid heavy exercise or large meals before testing to ensure accurate results.

Doctors order this test for many reasons, including routine health checkups, screening people who have a higher risk of kidney disease such as those with diabetes or high blood pressure, monitoring patients with known kidney problems, and checking kidney function before starting medications that can affect the kidneys.

Doctors use creatinine tests to diagnose and monitor kidney disease, evaluate kidney function after surgery or injury, check for dehydration, and assess how well medications are being processed by the kidneys.

Your results are usually reported in mg/dL and compared with a normal range that can vary slightly by laboratory, as well as by your age, sex, and muscle mass. A high level may mean your kidneys are not filtering as well as they should, while a low level is less common and may be related to reduced muscle mass. Your doctor will interpret your value along with other tests, such as eGFR, to give you a complete picture of your kidney health.

Results are interpreted in relation to your overall health, age, and other medical conditions. Elevated levels may signal reduced kidney function, while persistently low levels could warrant further investigation for underlying causes.