Creatinine, Serum

What is Creatinine?

Creatinine is a byproduct of a chemical compound called creatine, which helps muscles get the energy that they need. As a waste product, creatinine is filtered out of the blood by the kidneys and removed from the body in urine.

What is a Creatinine test used for?

A creatinine test measures the amount of this chemical in either the blood or urine. Creatinine levels can provide an indication of how well the kidneys are working. It's often ordered along with another kidney test called blood urea nitrogen (BUN) or as part of a comprehensive metabolic panel (CMP). A CMP is a group of tests that provide information about different organs and systems in the body. A CMP is frequently included in a routine checkup. Creatinine can also be measured with a urine test.

…more on kidneys:

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. 

What is the purpose of a creatinine test?

The primary use of a creatinine test is to better understand how well the kidneys are working. A measurement of creatinine can be employed for screening, diagnosis, and/or monitoring of kidney problems. 

Screening is trying to identify health problems before there are any signs or symptoms. If you are at higher risk of kidney problems, a creatinine test may be used to try to detect a problem early.

Diagnosis involves testing to determine the underlying cause after signs and/or symptoms have developed. Creatinine may be measured to help diagnose symptoms that can be associated with kidney problems, such as swelling in the feet, urinary changes, loss of appetite, and fatigue. A measurement of creatinine may also be included in a panel of tests for more general symptoms or when evaluating you in the emergency room.

Monitoring is how doctors track your condition over time. If you have kidney disease, a creatinine test can explain how the disease may progress. Tests of kidney function can also be used to watch for potential side effects when you have prescribed medications that can affect the kidneys.

In many cases, screening, diagnosis, and monitoring kidney problems involve more than just a creatinine measurement. For example, creatinine may be tested to calculate the estimated glomerular filtration rate (eGFR), which assesses how effectively the kidneys filter the blood.

Why do you need a creatinine test?

You may need this test if you have symptoms of kidney disease. 

These include:

- Fatigue and trouble sleeping

- Loss of appetite

- Puffiness around the eyes / swelling in the face, wrists, feet/ankles, or abdomen

- Swelling in your feet and/or ankles

- Decreased appetite

- Frequent and painful urination

- Urine that is foamy or bloody

- Lower back pain near the kidneys

- High blood pressure

- Nausea/vomiting

You may also need this test if you have certain risk factors for kidney disease. 

You may be at higher risk for kidney disease if you have:

- Type 1 or type 2 diabetes

- High blood pressure

- A family history of kidney disease

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, such as an enlarged prostate

- 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

- Streptococcal infections, such as poststreptococcal glomerulonephritis

- Aminoglycoside medications, such as gentamicin (Garamycin, Gentasol), 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.

What are normal Creatinine results:

Creatinine tests are generally used to assess kidney function. Under normal circumstances, creatinine levels are stable, reflecting typical muscle activity and the filtering and removal of creatinine from the bloodstream.

A normal result is 0.7 to 1.3 mg/dL (61.9 to 114.9 µmol/L) for men and 0.5 to 1.1 mg/dL (53 to 97.2 µmol/L) for women.

Why are female results often lower than male results?

Women often have a lower creatinine level than men. This is because women often have less muscle mass than men. Creatinine level varies based on a person's size and muscle mass.

Note on reference ranges:

The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results. There is no single reference range for all creatinine tests or for all people. Measurements can vary between laboratories, so it is important to look carefully at your test report to see the listed reference range for the lab that conducted your test. Creatinine’s reference range also depends on whether it is measured in the blood or urine.

A normal creatinine level does not guarantee kidney health. Moderate kidney impairment may not cause creatinine to rise to abnormal levels, so creatinine tests may not identify some cases of early kidney disease.

Additional notes:

When creatinine is measured in panel tests, it may be interpreted in conjunction with other test findings. For example, the amount of creatinine relative to blood urea nitrogen (BUN), another waste product, may provide useful information about the cause of kidney issues.

A number of individual factors, such as age, diet, and muscle mass, can affect creatinine levels, so it is important to remember your test should be interpreted with the help of your doctor in the context of your specific situation. This interpretation will also depend on why the test was ordered and whether you have any symptoms. Sometimes a doctor may prefer using a different test (such as Cystatin C) to assess a particular patient’s kidney function.

References:

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