Creatinine Blood Test (Normal, Low, High Levels)

The kidneys maintain the blood creatinine in a normal range. Creatinine is a fairly reliable indicator of kidney function. Elevated creatinine level signifies impaired kidney function or kidney disease.

As the kidneys become impaired for any reason, the creatinine level in the blood will rise due to poor clearance of creatinine by the kidneys. Abnormally high levels of creatinine thus warn of possible malfunction or failure of the kidneys. It is for this reason that standard blood tests routinely check the amount of creatinine in the blood.

A more precise measure of kidney function can be estimated by calculating how much creatinine is cleared from the body by the kidneys. This is referred to as creatinine clearance and it estimates the rate of filtration by kidneys (glomerular filtration rate, or GFR). The creatinine clearance can be measured in two ways.

• It can be calculated (estimated) by a formula using serum (blood) creatinine level, patient's weight, and age. The formula is 140 minus the patient's age in years times their weight in kilograms (times 0.85 for women), divided by 72 times the serum creatinine level in mg/dL.
• Creatinine clearance can also be more directly measured by collecting a 24-hour urine sample and then drawing a blood sample. The creatinine levels in both urine and blood are determined and compared.

Normal creatinine clearance for healthy women is 88-128 mL/min. and 97 to 137 mL/min. in males (normal levels may vary slightly between labs).

Blood urea nitrogen (BUN) level is another indicator of kidney function. Urea is also a metabolic byproduct that can build up if kidney function is impaired. The BUN-to-creatinine ratio generally provides more precise information about kidney function and its possible underlying cause compared with creatinine level alone. BUN also increases with dehydration.

Normal levels of creatinine in the blood are approximately 0.6 to 1.2 milligrams (mg) per deciliter (dL) in adult males and 0.5 to 1.1 milligrams per deciliter in adult females. (In the metric system, a milligram is a unit of weight equal to one-thousandth of a gram, and a deciliter is a unit of volume equal to one-tenth of a liter.)

• A person with only one kidney may have a normal level of about 1.8 or 1.9.
• High creatinine levels that reach 2.0 or more in babies and 5.0 or more in adults may indicate severe kidney impairment.
• The need for a dialysis machine to remove wastes from the blood is based upon several considerations including the BUN, creatinine level, potassium level, and how much fluid the patient is retaining.
• Low creatinine levels indicate malnutrition, severe weight loss, long term illness, and low muscle mass such as in the elderly and infant

The symptoms of kidney dysfunction (renal insufficiency) vary widely. They generally do not correlate with the level of creatinine in the blood.

• Some people may have an incidental finding of severe kidney disease and elevated creatinine on routine blood work without having any symptoms.
• In others, depending on the cause of the problem, different symptoms of kidney failure may be present including:
  • feeling dehydrated,
  • fatigue,
  • loss of appetite,
  • Insomnia,
  • excessive urination or lower than normal urination,
  • swelling (edema),
  • shortness of breath,
  • confusion, or
  • many other nonspecific symptoms (for example, nausea, vomiting, neuropathy, and dry skin).

Any condition that impairs the function of the kidneys is likely to raise the creatinine level in the blood. It is important to recognize whether the process leading to kidney dysfunction (kidney failure, azotemia) is longstanding or recent. Recent elevations may be more easily treated and reversed.

The most common causes of longstanding (chronic) kidney disease in adults are

• high blood pressure and
• diabetes.

Other causes of elevated blood creatinine levels are:

• Certain drugs (for example, cimetidine [Bactrim]) can sometimes cause abnormally elevated creatinine levels.
• Serum creatinine can also transiently increase after ingestion of a large amount of dietary meat; thus, nutrition can sometimes play a role in creatinine measurement.
• Kidney infections, rhabdomyolysis (abnormal muscle breakdown), and urinary tract obstruction may also elevate creatinine levels.

• Muscular young or middle-aged adults may have more creatinine in their blood than the norm for the general population.
• Elderly persons may have less creatinine in their blood than the norm. 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.