Creatinine Blood Test

The creatinine blood test may indicate severe kidney problems if creatinine levels are too high.

Creatinine is a waste product in the body that comes from the normal breakdown of muscle tissue and the digestion of proteins in your diet. This waste product is normally removed from the body by the kidneys. It is normal to have creatinine in the bloodstream, but high levels can signal that there is a problem with kidney function. The creatinine blood test measures the level of creatinine in your blood.

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 (removal) 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, and why the creatinine blood test is so important.

The amount of creatinine itself can be measured in the blood or the urine. 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 called creatinine clearance and estimates the filtration rate by kidneys (glomerular filtration rate, or GFR).

The creatinine clearance can be measured in two ways:

1. 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.
2. Creatinine clearance can also be more directly measured by collecting a 24-hour urine sample and drawing a blood sample. The creatinine levels in both urine and blood are determined and compared.

Blood urea nitrogen (BUN) level is another indicator of kidney function. Urea is a metabolic byproduct that can also 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 creatinine levels in the blood are approximately 0.7 to 1.3 milligrams (mg) per deciliter (dL) in adult males and 0.6 to 1.1 milligrams per deciliter in adult females. Normal values will vary slightly across different laboratories. There also may be slight variations by race.

A person with only one kidney may have a normal level of about 1.8 or 1.9.

Normal creatinine levels by age vary as children and babies typically have lower levels than adults.

Similarly to the creatinine blood test, creatinine clearance, as mentioned above, is another test that is used to assess kidney function. This test measures how well the kidneys filter out creatinine over a given period. Instead of a blood sample, creatinine clearance is usually determined from a measurement of creatinine in a 24-hour urine sample and from a blood sample taken during the same time. Creatinine clearance is reported as milliliters of creatinine per minute per body surface area (mL/min/BSA).

The table below shows the normal values of creatinine clearance by age group.

In general, any creatinine measurement over 1.3 is abnormally high. Low levels of creatinine (below the reference range for the laboratory) are sometimes seen in people with low muscle mass. Low creatinine levels are typically not a problem.

What level of creatinine is concerning?

High creatinine levels that reach 2.0 or more in babies and 5.0 or more in adults may indicate severe kidney impairment. Any creatinine blood test level that is over 1.3 should be investigated to determine the cause.

High creatinine blood test levels

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
• Diabetes

Other causes of elevated blood creatinine levels are:

• Certain drugs (for example, cimetidine [Tagamet] and trimethoprim-sulfamethoxazole [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.

Low creatinine blood test levels

Low creatinine levels indicate and may be caused by the following:

• Malnutrition
• Severe weight loss
• Long-term illness
• Low muscle mass such as in the elderly and infant

The following factors may result in a high or low creatinine blood test reading:

• 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 mg/dL 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.

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
• Many other nonspecific symptoms (for example, nausea, vomiting, neuropathy, and dry skin)

Creatine can be measured in both blood and urine in the following ways:

Blood creatinine normal range

A blood sample is collected from a vein and sent to the lab for analysis.

The normal range of creatinine levels in the blood are:

• Males: 0.7 to 1.3 mg/dL.
• Females: 0.6 to 1.1 mg/dL.

Urine creatinine normal range

A urine sample is collected early in the morning and sent for analysis.

The normal range of creatinine levels in urine varies according to age and muscle mass, but in general, are:

• Males: 995 to 2936 mg/24 hours.
• Females: 601 to 1689 mg/24 hours.

High creatinine levels can be caused by a variety of factors, and the symptoms may differ depending on the etiology. Treatment is directed at the underlying cause of the kidney dysfunction.

• In many circumstances, drugs can help alleviate excessive creatinine levels by addressing the underlying disease.
• Drugs to treat high blood pressure may help the endothelial damage seen in the renal blood vessels in diabetes and hypertension.
• Plenty of hydration and dietary restrictions on sodium, protein, and uric acid-containing foods are a must.

Dialysis, in addition to drugs, helps to filter toxins and waste products from the blood could be necessary in cases of renal failure. A kidney transplant may be required in severe or end-stage cases.

Drinking water can only lower creatinine levels when the elevated level is due to dehydration. People who have symptoms of dehydration (thirst, fatigue, dizziness) may have artificially high creatinine levels that can be corrected by restoring the body’s normal water content. For people who are not dehydrated, drinking water will not lower creatinine.

Eating less red meat and fewer fish products may reduce high creatinine levels in some people, but if underlying kidney disease is present, these dietary changes will not cure the underlying condition.

The prognosis for high or low creatinine blood test levels depends on the cause. Low creatinine is often found in people who have lost muscle mass or who have low muscle mass. While the low levels themselves will not cause medical problems, the underlying condition, such as malnutrition or chronic disease, will determine the person's overall prognosis.

In people with high creatinine levels, the prognosis depends on the reason for the kidney dysfunction. Some temporary causes, such as acute or recent illnesses, may be treated and may have a better prognosis than chronic kidney failure. With chronic kidney disease, the prognosis depends on the severity of the condition. Maintaining good control over blood pressure and keeping blood sugar under control in people with diabetes can decrease the chances of developing chronic renal failure.

Any high creatinine level shown in a creatinine blood test should be investigated to determine the cause. Many kidney conditions may be treated or effectively managed over time. As previously noted, creatinine levels of 5.0 or greater in an adult typically signify severe kidney failure.

Low levels of creatinine that develop from malnutrition may sometimes be prevented by maintaining adequate nutrition. Low creatinine due to chronic disease is only preventable if the underlying disease is preventable.

Kidney dysfunction can often be prevented in people with diabetes by maintaining good control of their diabetes. In people with elevated blood pressure, keeping blood pressure under control with diet, lifestyle changes, and/or medications can help prevent kidney dysfunction from developing. Some causes of kidney disease that lead to high creatinine levels may not be preventable.