Creatinine: What Is It, Normal Levels & When to Worry

Creatinine is a substance that is produced by the muscles, circulates in the blood and, then is eliminated by the kidneys. Creatinine levels can be analyzed to investigate for problems in the kidneys, which will usually cause higher levels of creatinine. 

Creatinine tests are ordered by a a family doctor or urologist as part of a routine exam or when there are signs or symptoms that may suggest a renal abnormality, like excessive fatigue, increased urine output, swelling or lower back pain.

The doctor can order for creatinine blood testing or a 24-hour urine test, which looks at how much creatinine was eliminated through the urine over the course of a day. Learn more about creatinine clearance tests and how they are done.

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Normal levels 

Normal reference values for creatinine can vary from lab to lab, depending on the lab method used to to analyze the specimen. Because creatinine is produced by the muscles, its levels in the blood can range in children as they grow, and therefore reference ranges vary depending on age:  

  • Newborns: 0.60 to 1.30 mg/dL
  • Babies between 1 and 6 months: 0.40 to 0.60 mg/dL
  • Children and teens (between 1 and 18 years old): 0.4 to 0.90 mg/dL

Creatinine levels can also depend on your sex:

  • Women: 0.60 to 1.2 mg/dL
  • Men: 0.70 to 1.3 mg/dL

Creatinine levels will also depend on your muscle mass. Because men typically have more muscle mass, they are expected to have higher creatinine levels in comparison to women. 

High creatinine levels 

Elevated creatinine levels in the blood are a sign of a kidney abnormality, like an injury to a blood vessel, a kidney infection, or decreased blood flow to the kidneys. This can happen with medications, increased protein intake, kidney stones or chronic diseases like hypertension or unmanaged diabetes. 

Athletes may be noted to have higher creatinine levels due to intense physical activity. Their higher levels are unrelated to kidney issues.

Read more about what can cause high creatinine levels and the symptoms that high levels can lead to. 

Low creatinine levels 

Low creatinine levels are not a significant finding and are especially common in pregnant women and patients with a history of liver disease, as the liver is also responsible for the production of creatinine. 

In some people, very low levels may be a sign of a muscle disease, such as muscular dystrophy, which is associated with muscular pain and difficulty moving the arms or legs. 

When to worry

A creatinine test can be ordered by a doctor or urologist to evaluate kidney function, especially when a patient presents with symptoms like excessive fatigue, loss of appetite, lower back pain, or changes to urinary frequency and daily output.  Therefore, if you notice any of these symptoms, you should see your doctor for assessment. Read more about symptoms of kidney problems and when to seek medical attention. 

Elevated levels in the blood are usually a sign of altered kidney function, and your doctor may advise you to start on medication to boost filtering capacities in the kidneys. Some medication, like cimetidine, aspirin, ibuprofen and cephalosporin, may be discontinued.

In the presence of high blood levels, the doctor may also opt to order a 24 hour urine test to analyze the amount of creatinine eliminated in the urine over one day. The amount of creatinine in the urine is then compared to levels in the blood. Because creatinine is unable to be eliminated, creatinine levels in the blood are expected to be higher than levels in the urine.