Creatinine in Whole Blood (Serum/Plasma)

Why Is This Test Done?

Doctors may order a creatinine test to check how well your kidneys are filtering waste from your blood. It’s often used alongside other tests like blood urea nitrogen (BUN) to evaluate kidney function, especially if you have symptoms like swelling, fatigue, or changes in urine output. It can also be part of routine check-ups for people with risk factors, such as high blood pressure or diabetes.

What to Expect Before the Test

You’ll typically have a small needle inserted into your arm for a blood draw. No special preparation is needed, but avoid strenuous activity or eating/drinking for 8–12 hours before if instructed by your provider. Hydration may be encouraged, but check with your doctor first.

What the Results Mean

Creatinine levels can vary based on factors like muscle mass, age, and hydration status. Higher levels may suggest impaired kidney function, while lower levels might indicate overhydration or other conditions. Your doctor will interpret results in relation to your overall health and other tests.

Common Causes of Abnormal Results

Elevated creatinine can result from kidney disease, dehydration, or conditions that reduce blood flow to the kidneys. Lower levels may occur with overhydration, certain medications, or liver/kidney disorders. Always discuss results with your healthcare provider.