Serum or Plasma Creatinine (Mass Concentration)

Why Is This Test Done?

Your doctor may order this test to check for kidney disease, monitor kidney function over time, or evaluate symptoms like swelling, fatigue, or changes in urine output. It’s also used before certain procedures or medications to ensure your kidneys are working properly.

What Does a Result Mean?

Higher-than-normal levels may indicate kidney problems, dehydration, or conditions that increase muscle breakdown. Lower-than-normal levels could suggest overhydration or certain liver/kidney disorders, though this is less common. Results alone don’t diagnose kidney disease—your doctor will consider other factors.

Sample Collection and Preparation

A blood sample is drawn from a vein, usually in your arm. If you’re on dialysis or have a central line, a different vein may be used. Plasma (if drawn without an anticoagulant) or serum (if drawn with a clot activator) is used. Avoid strenuous activity or heavy meals 12 hours before testing to help ensure accurate results.

Common Causes of Abnormal Results

Factors like muscle injury, heart failure, dehydration, or certain medications can temporarily raise creatinine levels. Conversely, overhydration or conditions affecting muscle metabolism may lower it. Chronic kidney disease, diabetes, or high blood pressure often show persistent changes over time.