Understanding Your Lab Values: Creatinine test

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According to a recent study, reported at the annual meeting of American Society of Nephrology in San Diego. primary care physicians are failing to diagnose chronic kidney disease, especially in women.

Study leader Dr. Maya Rao of Columbia University in New York says primary care doctors typically order a blood test called creatinine to measure kidney function, but this alone is not a particularly accurate measure of kidney function.

Glomerular filtration rate (GFR) is the best test to measure your level of kidney function and determine your stage of kidney disease.
You can calculate your Glomerular Filtration Rate (GFR), by entering results of your blood creatinine test, your age, race, gender and other factors.

The distribution of creatinine test results in 6434 people is shown on the right (NHANES 2006 study, weighted for USA demographics, graph by WolframAlpha)

The typical reference ranges in adult males are 0.7 to 1.2 mg/dL according to Wikipedia and 0.6 to 1.2 milligrams (mg) per deciliter (dl) according to medicinenet. In adult females, it's 0.5 to 1.1 milligrams per deciliter (wikipedia) or 0.5 to 1.1 mg/dl (medicinenet). LabCorps lists normal values between 0.57 and 1.00 mg/dL. (see also reference values for other medical tests and Aurametrix blog on liver tests). Men tend to have higher levels of creatinine because they generally have more skeletal muscle mass than women. Muscular young or middle-aged adults may have more creatinine in their blood than the norm for the general population. Vegetarians have been shown to have lower creatinine levels. Creatinine tends to be slightly lower in pregnancy. It increases with height and body weight. While a baseline serum creatinine of 2.0 mg/dL (150 μmol/l) may indicate normal kidney function in a male body builder, a serum creatinine of 0.7 mg/dL (60 μmol/l) can indicate significant renal disease in a frail old woman.

Infants have normal levels of about 0.2 or more, depending on their muscle development. In people with malnutrition, severe weight loss, and long standing illnesses the muscle mass tends to diminish over time and, therefore, their creatinine level may be lower than expected for their age.

A person with only one kidney may have a normal level of about 1.8 or 1.9. Creatinine levels that reach 2.0 or more in babies and 10.0 or more in adults may indicate severe kidney impairment and the need for a dialysis machine to remove wastes from the blood.

In the United States, creatinine is typically reported in mg/dL, while in Canada and Europe μmol/litre may be used. 1 mg/dL of creatinine is 88.4 μmol/l.

Creatinine is a waste product in your blood that comes from muscle activity. It is normally removed from your blood by your kidneys, but when kidney function slows down, the creatinine level rises.

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