A creatinine blood test measures the level of creatinine in the blood. Creatinine is a waste product that forms when creatine breaks down. Creatine is found in your muscle. Creatinine levels in the blood can provide your doctor with information about how well your kidneys are working.
The kidneys are a pair of fist-sized organs located at the bottom of the rib cage. One kidney is on each side of the spine. Each kidney has millions of small blood-filtering units called nephrons. The nephrons constantly filter blood through a very tiny cluster of blood vessels known as glomeruli. These structures filter waste products, excess water, and other impurities out of the blood. The toxins are stored in the bladder and then removed during urination.
Creatinine is one of the substances that your kidneys normally eliminate from the body. Doctors measure the level of creatinine in the blood to check kidney function. High levels of creatinine may indicate that your kidney is damaged and not working properly.
Creatinine blood tests are usually performed along with several other laboratory tests, including a blood urea nitrogen (BUN) test and a basic metabolic panel (BMP) or comprehensive metabolic panel (CMP). These tests are done during routine physical exams to help diagnose certain diseases and to check for any problems with your kidney function.
Your doctor may order a creatinine blood test to assess your creatinine levels if you show signs of kidney disease. These symptoms include:
- fatigue and trouble sleeping
- a loss of appetite
- swelling in the face, wrists, ankles, or abdomen
- lower back pain near the kidneys
- changes in urine output and frequency
- high blood pressure
Kidney problems can be related to different diseases or conditions, including:
- glomerulonephritis, which is an inflammation of the glomeruli due to damage
- pyelonephritis, which is a bacterial infection of the kidneys
- prostate disease
- blockage of the urinary tract, which may be due to kidney stones
- decreased blood flow to the kidneys, which may be caused by congestive heart failure, diabetes, or dehydration
- the death of kidney cells as a result of drug abuse
Aminoglycoside medications, such as gentamycin, can also cause kidney damage in some people. If you’re taking this type of medication, your doctor may order regular creatinine blood tests to make sure your kidneys remain healthy.
A creatinine blood test doesn’t require very much preparation. However, it’s important to tell your doctor about any prescription or over-the-counter medications you’re currently taking. Some drugs may increase your creatinine levels without causing kidney damage and interfere with your test results. Let your doctor know if you take:
- nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin or ibuprofen
- chemotherapy drugs
Your doctor may ask you to stop taking your medication or to adjust your dosage before the test. They’ll also take this into consideration when interpreting your test results.
The creatinine blood test is a simple test that requires the removal of a small sample of blood.
A technician called a phlebotomist will ask you to pull up your sleeves so that your arm is exposed. They’ll sterilize the injection site with an antiseptic and then tie a band around your arm. This makes the veins swell with blood, allowing them to find a vein more easily. Once they find a vein, they’ll insert a needle into it to collect the blood. In most cases, a vein on the inside of the elbow is used. You might feel a slight prick when the needle is inserted, but the test itself isn’t painful. After the phlebotomist removes the needle, they’ll put a bandage over the puncture wound.
A creatinine blood test is a low-risk procedure. However, there are some minor risks, including:
- fainting at the sight of blood
- dizziness or vertigo
- soreness or redness at the puncture site
Once enough blood is drawn, the sample is sent to a laboratory for analysis. Your doctor will give you the results within a few days of testing.
Creatinine is measured in milligrams per deciliter of blood (mg/dL). People who are more muscular tend to have higher creatinine levels. Results may also vary depending on age and gender.
In general, however, normal creatinine levels range from 0.7 to 1.3 mg/dL in men and 0.6 to 1.1 mg/dL in women.
High serum creatinine levels in the blood indicate that the kidneys aren’t functioning properly.
Your serum creatinine levels may be slightly elevated or higher than normal due to:
- a blocked urinary tract
- a high-protein diet
- kidney problems, such as kidney damage or infection
- reduced blood flow to the kidneys due to shock, congestive heart failure, or complications of diabetes
It’s uncommon to have low levels of creatinine, but this can occur as a result of certain conditions that cause decreased muscle mass. They’re usually not any cause for concern.
It’s important to note that normal and abnormal ranges can vary among labs because some use unique measurements or test different samples. You should always meet with your doctor to discuss your test results in more detail. They’ll be able to tell you if more testing is necessary and if any treatment will be required.