Level of creatinine in blood and urine is often checked to analyze the functioning of kidneys. Here is a brief overview about these diagnostic tests.
Creatine (not creatinine) is an organic acid produced in the body of vertebrates, and is mainly found in the skeletal muscles. Creatine is involved in muscle metabolism, which produces creatinine as a waste product. Around 2% of the creatine in the body is converted into creatinine daily. The blood carries this creatinine to the kidneys, which in turn filter and expel it out of the body through urine, in very small amounts.
The body does not reabsorb creatinine from the kidneys or even from the blood. So if the kidneys fail to function properly, the creatinine level in the blood rises. In that case, the amount of creatinine in the urine drops, simultaneously. As the muscle mass of a person does not change on a daily basis, the creatinine levels will be almost constant in normal people. Hence, a high level of creatinine in the blood indicate health problems, mainly relating to the kidneys.
Normally, a routine blood or urine test shows the level of creatinine. However, creatinine clearance test is considered to be more accurate, as it provides a better picture of the kidney function. This test is done on both blood and urine samples, collected over a time span of 24 hours. Along with these tests, a blood test to determine the BUN-to-creatinine ratio is also done, to assess the function of the kidneys. Given below are the normal values for blood creatinine test, creatinine clearance test, and the blood test for detecting the BUN-to-creatinine ratio.
Blood Creatinine Test
- In adult males, the normal levels of blood creatinine should be between 0.6 to 1.2 mg/dl (milligrams per deciliter). In adult females the normal range is 0.5 to 1.1 mg/dl.
- In infants, the normal blood creatinine level is 0.2 mg/dl or more. This figure may vary slightly according to their muscle development. Children have a blood creatinine level of around 0.3 to 0.7 mg/dl.
- The normal level of blood creatinine in teenagers is around 0.5 to 1.0 mg/dl, and elderly people tend to have lower levels.
- If a person has only one kidney, the normal blood creatinine level can range between 1.8 or 1.9 mg/dl.
Creatinine Clearance: In case of creatinine clearance tests, the normal range for men below the age of 40, is around 107 to 139 mL/min (milliliters per minute); and for women (below 40 years), it is 87 to 107 mL/min. The value of creatinine clearance is found to be lower in elderly people. It is said that, the value may reduce by 6.5 mL/min, for every 10 years, after the age of 20.
The normal BUN-to-creatinine ratio ranges between 6 to 25, in adults. However, these values can be affected by various other factors, such as age, gender, and amount of muscle mass. Some medication can also temporarily elevate creatinine levels in blood. According to health experts, consumption of dietary meat in large quantities can also cause changes in the creatinine level. Other such factors include strenuous exercises, excess intake of caffeine, etc.
The level of creatinine in blood should not rise beyond 2.0 mg/dl or more in babies and 10.0 in adults. Such high levels of blood creatinine may indicate serious kidney damage, which is mainly caused by high blood pressure and diabetes. While kidney damage can be caused by various health problems, there are other medical conditions, which result in high blood creatinine levels. They include gout, excessive blood loss, dehydration, heart failure, rhabdomyolysis, polymyositis, myasthenia gravis, acromegaly, and gigantism.
Even low levels of blood creatinine can point towards some health problems, like muscular dystrophy or severe liver diseases. In some cases, pregnancy or a low-protein diet can also cause low creatinine levels. Level of creatinine can be lowered by drinking more water, avoiding high-protein food, and dairy products; and by testing the blood and urine, periodically. So, if your routine blood test shows such abnormal levels of blood creatinine, then you must consult a doctor at the earliest, to avoid complications.
As far as creatinine clearance values are concerned, a high level is usually seen in pregnant women, and those with hypothyroidism. Low values indicate severe kidney problems. Diseases of the liver and heart may also lead to low creatinine clearance levels. A high BUN-to-creatinine ratio may be caused by kidney failure, or bleeding in the gastrointestinal or respiratory tract. A low value is often seen in pregnant women and those with rhabdomyolysis and cirrhosis. A low-protein diet may also lead to such low values.
Disclaimer: This article is for informational purposes only and should not be used as a replacement for expert medical advice. Visiting your physician is the safest way to diagnose and treat any health condition.