Creatinine

Creatinine is a waste product that comes from the digestion of protein in your food and the normal breakdown of muscle tissue. It is removed from the blood through your kidneys. Everyone has some creatinine in their blood, but too much can be a sign of a possible kidney problem.

The serum (blood) creatinine test is a blood test used to check how well your kidneys are filtering your blood. It is usually ordered in combination with other tests as part of a bundle called the “basic metabolic panel” (BMP) or “comprehensive metabolic panel” (CMP). It is one of the most frequently ordered lab tests and is often part of a routine health check.

The serum (blood) creatinine test is often used in the following situations:

• To check kidney health in people at high risk for chronic kidney disease (CKD) or for people with symptoms of acute kidney injury (AKI)
• To monitor changes in kidney function over time in people living with CKD
• To help your healthcare professional decide if any of your medications need to be stopped or changed to a lower dose

There is very little risk with this blood test. You may have slight pain or bruising at the spot where the needle is put in, but most symptoms go away quickly.

Most people do not have to take any special steps before having this lab test done. Ask your healthcare professional if there are any special instructions to follow. You may be asked to avoid eating or drinking anything (except water) for several hours before the test. In some less common situations, you may also be asked not to eat any cooked meat the night before the test. Cooked meat can increase the level of creatinine in your blood and affect your eGFR results.

A healthcare professional will take a small amount of blood from a vein in your arm, using a small needle. You may feel a little sting when the needle goes in or out. This test usually takes less than five minutes.

There are typically no restrictions after completing this test.

Although serum (blood) creatinine is a very common test, only looking at your creatinine level is not the best way to understand your kidney health. This is because a “normal” creatinine level in the blood can change depending on your age, sex, body size, and other factors.

Some people with a “normal” creatinine level as reported in their lab results may actually have kidney disease. The opposite can also be true – some people with a “high” creatinine level may not have kidney disease, or it may be less severe than it seems.

So, the best way to know how well your kidneys are working is to look at your estimated glomerular filtration rate (eGFR). Your eGFR is calculated using your serum (blood) creatinine level, age, and sex. It can also be calculated using your cystatin C level instead of or in addition to your serum (blood) creatinine level. An eGFR calculated using both your serum (blood) creatinine and cystatin C levels is more accurate than using either lab value by itself.

Your serum (blood) creatinine level is a very effective test for checking your kidney health. However, there may be other factors that can cause higher or lower creatinine levels in your blood that are not related to your kidney health. In other words, your actual kidney function (eGFR level) may be higher or lower than what is reported in your lab results.

Some factors that can lead to higher creatinine levels (making your eGFR level appear lower than it might really be) include:

• Eating large amounts of cooked meats
• Taking creatine supplements
• Recent high intensity exercise
• High muscle mass (very muscular body frame, bodybuilder)
• Taking medications such as cimetidine, cobicistat, dolutegravir, fenofibrate, ritonavir, or trimethoprim

Some factors that can lead to lower creatinine levels (making your eGFR level appear higher than it might really be) include:

• Following a vegan or vegetarian diet
• Low muscle mass
• Pregnancy
• History of an amputation or muscle wasting disease
• Severe liver disease (cirrhosis)

The actual effect that these factors may have on a person’s serum (blood) creatinine level is highly variable. In other words, everyone responds very differently to these factors. So, it is very important to talk with your healthcare professional if you have concerns about interpreting your serum (blood) creatinine or eGFR level.

• When was the last time I had a serum (blood) creatinine test completed?
• What is my eGFR level based off my most recent serum (blood) creatinine level?
• When should my serum (blood) creatinine be checked again?
• Do I have any factors that might make my creatinine levels higher or lower than expected? What does this mean for how I should interpret my eGFR (kidney function) test?

• Stages of chronic kidney disease
• Are you at increased risk for chronic kidney disease?
• Estimated glomerular filtration rate
• Acute kidney injury
• Tests to check your kidney health