Serum Creatinine (for Transplant Evaluation)

Why is this test done? Doctors order a creatinine test to measure how well your kidneys are filtering waste from your blood. Creatinine is a waste product your muscles make at a steady rate, and healthy kidneys remove it from your body. This test helps diagnose or monitor kidney disease, check for dehydration, and follow the effects of conditions such as high blood pressure or diabetes.

Your doctor may order this test to evaluate kidney function, especially if you’re on a transplant waiting list. Creatinine levels help assess how well your kidneys are filtering waste from your blood, which is critical for determining transplant eligibility and monitoring post-transplant health.

A high creatinine level may mean your kidneys are not clearing waste as well as they should, which can happen with kidney disease, dehydration, a urinary tract blockage, or certain medicines. A low level is less common and may be linked to reduced muscle mass, poor nutrition, or pregnancy. Your doctor will look at your result together with other tests to find the cause.

High creatinine levels may indicate poor kidney function, while low levels could suggest overhydration or other conditions. Since reference ranges vary by age, sex, and muscle mass, your results will be interpreted in the context of your overall health.

This test is most often done with a simple blood draw. A health care provider will clean the skin on your arm, wrap a band around your upper arm, and use a small needle to collect a blood sample from a vein. Sometimes creatinine is measured in urine instead, using either a single sample or all the urine you collect over a 24-hour period.

A blood sample is taken from a vein, usually in your arm. The sample is sent to a lab where creatinine is measured using an automated method that detects waste products in your blood.

Most people do not need special preparation for a creatinine blood test. Your doctor may ask you to avoid eating large amounts of meat for 24 hours beforehand and to drink water as usual. Tell your provider about all medicines and supplements you take, because some can affect the results. If a 24-hour urine test is needed, your care team will give you detailed instructions.

Avoid heavy exercise or dehydration 24 hours before the test. If you’re on a transplant waitlist, follow your healthcare team’s specific instructions, as some tests may require fasting or other preparations.