Serum Creatinine Test: Why and How is it Done?

Creatinine is a waste product that is produced from normal body muscle wear and tear. There is creatinine in everybody’s bloodstream. The serum creatinine test is done to measure the amount of creatinine in the blood. This examination is conducted to see how well the kidneys function. A urine test may also measure creatinine.

Each kidney has millions of tiny units of blood filtering known as nephrons. The nephrons pump blood continuously through a very small network of blood vessels known as glomeruli. Those structures filter out of the blood – waste products, toxins, excess water, and other impurities. The contaminants are contained in the bladder and exit the body when urinating.

Normally, creatinine is one of the substances which healthy kidneys remove from the body. And so doctors measure creatinine levels in the blood to evaluate kidney function. High creatinine levels may suggest damage to your kidney, and that they may not be functioning properly.

The creatinine test is generally performed along with various other laboratory tests, including a blood urea nitrogen (BUN) test and a rudimentary metabolic panel (BMP) or comprehensive metabolic panel (CMP). At routine physical exams, these tests are done to help diagnose certain conditions and to check for any kidney function problems.

Why is the serum creatinine test done?

A serum creatinine test — measuring the creatinine level in your blood — can determine whether your kidneys are working well.

How often a creatinine test is required to be repeated depends on underlying conditions and your risk of damage to the kidneys. For instance: 

• Your doctor may advise you to have your creatinine test done a minimum of once a year if you are a type 1 or type 2 diabetes.
• You might have to undergo a creatinine test if you have any medical condition that might affect your kidneys, such as diabetes and high blood pressure or if you are taking medication that might affect your kidneys. 
• Your medical expert might ask you to do a serum creatinine test if you have symptoms that point out probable kidney problems. 

Prerequisites of a Serum Creatinine Test

You might be told not to eat cooked meat for at least 24 hours before the test. Studies have demonstrated that cooked meat can increase levels of creatinine temporarily. 

A  serum creatinine test alone needs no planning. Fasting is not normally needed, unless it is done together in a panel. To get the correct result, you would normally be advised to eat and drink the same as you usually do. 

Nonetheless, it is important to inform your doctor about any prescription or over-the-counter (OTC) medicines you are taking at present. Many medications will boost the level of creatinine without causing damage to the kidney and interfering with the test results.

If you take any of these medicines, let your doctor know:

• Cephalosporin antibiotics, such as cephalexin and cefuroxime 
• Nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin or ibuprofen 
• Chemotherapy drugs
• Cimetidine 

You may be asked by your doctor to stop taking your medicines or do some dosage adjustments before the test. The doctor will also take that into account when evaluating the test results.

Serum Creatinine Test: Understanding the Results

Creatinine is expressed in milligrams per blood deciliter (mg/dL). People who are more on the muscular side tend to have higher levels of creatinine. Results can also vary based on age and gender.

But in general, normal levels of creatinine range from 0.9 to 1.3 mg/dL in men, and from 0.6 to 1.1 mg/dL in women aged 18 to 60. Normal levels for people over 60 are about the same.

If you get high levels of serum creatinine in the blood, it could be a sign that your kidneys are not working properly.

Your serum creatinine levels may be slightly higher or higher than normal, because of possible conditions like:

• Kidney problems, such as kidney damage or infection
• Dehydration
• A high-protein diet
• A reduced flow of blood to the kidneys due to congestive heart failure, shock, or complications of diabetes
• A blocked urinary tract

If your creatinine is really high and is caused by an acute or chronic kidney injury, the amount will not decrease until the main problem is resolved. If it was briefly or wrongly elevated due to dehydration, a very high protein diet, or the use of supplements, then the amount will be reduced by removing such factors. A person receiving dialysis, after treatment, will also have lower levels.

Having low creatinine levels is rare, but this can happen as a result of certain conditions that cause reduced muscle mass. Normally, they are no cause for concern.

When should it be repeated?

After a few weeks, your doctor may want to repeat the serum creatinine test to see if the results are similar. If you have diabetes type 1 or type 2, your doctor may prescribe creatinine testing at least once a year.

If you suffer from renal disease, your doctor can recommend regular creatinine tests to monitor your condition.

Procedure

A member of your health care team takes a blood sample during the serum creatinine test by sticking a needle into a vein in your arm. Then, the blood sample will be sent to a laboratory for analysis. Once the test is done, you can immediately get back to your usual routine.

Your doctor may also in some cases measure the level of creatinine in your urine. For this test, which is a part of a creatinine clearance test, your doctor may ask you to collect urine samples for 24 hours in an exclusive container. The urinary creatinine test will help the doctor assess the existence or degree of kidney failure more accurately.

Learn more about diagnosing and managing kidney disease here.