Summarize this article:

Creatinine is a waste product produced by the body when creatine, a metabolism substance that helps convert food into energy, breaks down.  Usually, your kidneys help filter creatinine out of the blood. The waste product is then passed out of the body via urine. High creatinine levels can indicate a problem with your kidneys. High creatinine levels can be the result of regularly consuming a high amount of protein or partaking in strenuous exercise. Creatine supplements may also increase levels of creatinine in blood and urine. A creatinine test measures how much creatinine is in your blood.  Your doctor may also perform a creatinine clearance test, which measures the amount of creatinine in your urine. The amount in your blood should be low, and the amount in your urine should be high. These tests only provide a "snapshot" of your kidney health. They only measure the amount of creatinine in your blood and urine from one-time samples taken within the past 24 hours. The normal range for creatinine levels will vary based on whether you are an adult male, adult female, teenager, or child. The value you should be at may vary further based on your age and body size, but there are general ranges you should shoot for.  Normal blood creatinine levels are: Men: 0.6 to 1.2 mg/dL; 53 to 106 mcmol/L Women: 0.5 to 1.1 mg/dL; 44 to 97 mcmol/L Teenagers: 0.5 to 1.0 mg/dL Children: 0.3 to 0.7 mg/dL   Normal urine creatinine levels are:  Men: 107 to 139 mL/min; 1.8 to 2.3 mL/sec Women: 87 to 107 mL/min; 1.5 to 1.8 mL/sec Anyone above the age of 40: levels should drop by 6.5 mL/min for every additional 10 years of age There are several different reasons why you might have increased creatinine levels; some of these conditions are more severe than others, but all mean that you need to take steps to get your creatinine levels back to normal.  Renal failure or impairment: If your kidneys are damaged, they cannot filter creatinine out of your body through glomerular filtration as they are supposed to. Glomerular filtration is the outflow of filtered fluid passing through your kidney. Muscle destruction: If you have a condition that causes the breakdown of your muscles, the broken down muscle tissue can get into your bloodstream and impair your kidneys. High intake of meat: Eating a diet rich in cooked meat can increase the amount of creatinine in your body. Hypothyroidism: Having a dysfunction in your thyroid gland can have an influence on your kidney function. Hypothyroidism can decrease your kidneys’ ability to properly filter waste out of your body.

Summary:
Know what creatinine is. Understand how the test works. Interpret your results. Understand why increased creatinine levels occur.