Serum Creatinine (with optional 24-hour urine collection for glomerular filtration rate estimation)

Why This Test Matters

Creatinine is a byproduct of muscle breakdown and is filtered out of your blood by your kidneys. High levels can indicate kidney problems, while low levels might suggest overhydration or muscle loss. This test is often used alongside other measures to check kidney health, especially if you have symptoms like swelling, fatigue, or changes in urine output.

What to Expect Before the Test

You may be asked to fast for 8–12 hours before your blood draw, but this is not always required. If your doctor suggests a 24-hour urine test, you’ll need to collect all urine for a full day, starting after your first morning void. Drink plenty of water unless instructed otherwise.

Common Causes of Abnormal Results

Elevated creatinine levels can occur due to kidney disease, dehydration, severe muscle damage, or conditions that slow blood flow to the kidneys. Low levels may result from overhydration, liver disease, or certain medications. Your doctor will consider your overall health and other test results to interpret these findings.

What You Should Know About Results

Your doctor will compare your creatinine level to your age, sex, and body size. If your results are abnormal, they may recommend further tests, like a urine test or imaging, to investigate the cause. Never interpret results alone—always discuss them with your healthcare provider.