Creatinine Clearance

The purpose of the Creatinine Clearance test is to diagnose kidney malfunction

Both a urine sample (24-hour collection) and a blood sample drawn from a vein in your arm

Creatinine is normally filtered through the glomerulus – a group of blood vessels in the kidneys responsible for filtration. An abnormal kidney function test indicates that the patient may have lost more than 30-40% of his or her kidneys' function, which may be a permanent or temporary loss.

A decreased filtration rate may indicate a decrease in the amount of blood filtered by the kidney due to disease within the kidney cells or to decreased delivery of blood to the kidneys. Congestive heart failure, dehydration, shock, obstruction within the kidney, or acute or chronic kidney failure are among the possible causes.

As the amount of creatinine produced is proportionate to body size, your weight must be factored into the calculation. There are different normal ranges for males and females.

Certain drugs, such as aminoglycosides, cimetidine, cisplatin, and cephalosporins can decrease the creatinine clearance measurement. Diuretics can increase the result.

Creatinine

The purpose of the Creatinine test is t o determine if your kidneys are functioning normally and to monitor treatment for kidney disease.

It is used to determine whether your kidneys are functioning normally (in this case the amount of creatinine in your blood will be very low). A combination of blood and urine creatinine levels may be used to calculate a "creatinine clearance." This measures how effectively your kidneys are filtering small molecules like creatinine out of your blood.

Creatinine may be part of a basic metabolic panel , widely used when someone has non-specific health complaints, or it may be ordered if your doctor suspects kidney problems. The test is also used to monitor treatment of kidney disease or to monitor kidney function while you are on certain drugs.

Increased creatinine levels in the blood suggest diseases that affect kidney function. These can include:

• glomerulonephritis (swelling of the kidney's blood vessels);
• pyelonephritis (pus-forming infection of the kidneys);
• acute tubular necrosis (death of cells in the kidneys' small tubes); 
• urinary tract obstruction; or
• reduced blood flow to the kidney due to shock, dehydration , congestive heart failure , atherosclerosis , or complications of diabetes .

Creatinine can also increase as a result of muscle injury. Low levels of creatinine are not common and are not usually a cause for concern. They can be due to lack of height, decreased muscle mass, and some severe liver disease.

Since creatinine levels are in proportion to muscle mass, women tend to have lower levels than men.

In general, creatinine levels will stay the same if you eat a normal diet . However, eating large amounts of meat may cause short-lived increases in blood creatinine levels. Taking creatine supplements may also increase creatinine.

There are very few drugs that interfere with the creatinine test, although there are some drugs that can cause some impairment in kidney function. Your creatinine levels may be monitored if you are taking one of these drugs.

Microalbumin and Microalbumin/Creatinine Ratio

Also known as: Urine microalbumin, Albumin-to-Creatinine ratio

Formally known as: Microalbumin and Microalbumin/Creatinine Ratio

This test screens for a possible kidney disorder. Typically this test is performed annually after a diagnosis of diabetes or hypertension.

The random microalbumin test or microalbumin/creatinine ratio is frequently ordered as a screening test on patients with chronic conditions, such as diabetes and hypertension, that put them at an increased risk of developing kidney failure . Studies have shown that identifying the very early stages of kidney disease (microalbuminuria) helps patients and doctors adjust treatment. With better control of diabetes and hypertension, the progression of diabetic kidney disease can be slowed or prevented.

A timed microalbumin test (4 hour or overnight) may be ordered as an alternative screening tool. If significant amounts of microalbumin are detected with these screening tests, they may be confirmed with a 24-hour microalbumin test.

The National Kidney Foundation recommends that Type 2 diabetics under the age of 70 and Type 1 diabetics over the age of 12 be screened annually for microalbuminuria. In addition, microalbumin may be ordered when a person is first diagnosed with Type 2 diabetes . According to the American Diabetes Association, in Type 1 diabetes, annual testing should begin 5 years after diagnosis.

Patients with hypertension may be tested at regular intervals, with the frequency determined by their doctor.

Moderately increased microalbumin levels in urine indicate that a person is in one of the very early phases of developing kidney disease . Very high levels are an indication that kidney disease is present in a more severe form. Normal levels are an indication that kidney function is normal.

Recently, studies have shown that in Type 2 diabetics, an abnormal microalbumin result indicates an increased risk of developing cardiovascular disease (CVD) .

GFR and EGFR

Formally known as: Glomerular Filtration Rate and Estimated Glomerular Filtration Rate

The purpose of the GRF and EGFR test is to assess kidney function.

GFR is considered the most accurate way to detect changes in kidney status. While measurement of serum BUN (urea nitrogen) and creatinine are easier to do, they cannot pick up early damage to the kidneys. If kidney damage is detected early, it may be possible to prevent worsening damage to the kidneys with treatment of high blood pressure, diabetes , or other diseases that can damage the kidney. Because EGFR can be calculated based on serum creatinine, an easily performed and commonly used laboratory test, it is possible to get a close estimate of the actual GFR. Another method of estimating GFR (EGFR) involves the measurement of the serum level of a molecule called cystatin C . While this use of the test is gaining interest, this method is not yet widely used.

The EGFR calculation can be determined, with no extra testing, at the same time a sample is sent for creatinine . The National Kidney Foundation has recommended that it be calculated automatically every time a creatinine test is done. If you have had a creatinine measurement, you can calculate it yourself by using the “calculator” found on the National Kidney Foundation website at: http://www.kidney.org/kls/professionals/gfr_calculator.cfm.

GFR is usually measured if you are on an unusual diet or if you have protein or albumin in your urine.

EGFR can detect most types of kidney disease in their earliest changes. A normal EGFR means that kidney disease is unlikely. A low EGFR suggests that some kidney damage has occurred. GFR results are usually evaluated in the same way. Sometimes, in very early kidney damage (especially when the kidneys are damaged by diabetes ), EGFR and GFR may actually be high, indicating that the kidneys are working harder than normal.

The American Kidney Foundation has suggested that all persons “know their GFR number.”  They recommend interpreting GFR (usually by EGFR) based on the following table:

Please note: GFR and EGFR increase during pregnancy .

BUN

Formally known as: Blood Urea Nitrogen

The BUN level, usually with tests for creatinine , is used to evaluate kidney function and to monitor patients with kidney failure or those receiving dialysis therapy.

BUN is often ordered with creatinine:

• if kidney problems are suspected,
• to monitor treatment of kidney disease , or
• to monitor kidney function while someone is on certain drugs.

High BUN levels suggest impaired kidney function . This may be due to acute or chronic kidney disease. However, there are many things besides kidney disease that can affect BUN levels such as decreased blood flow to the kidneys as in congestive heart failure , shock, stress, recent heart attack or severe burns; conditions that cause obstruction of urine flow; or dehydration .

Low BUN levels are not common and are not usually a cause for concern. They can be seen in severe liver disease or malnutrition but are not used to diagnose or monitor these conditions. Low BUN is also seen in normal pregnancy .

BUN levels increase with age and also with the amount of protein in your diet . High-protein diets may cause abnormally high BUN levels. Very low-protein diets can cause abnormally low BUN. Lower BUN levels are also seen in infants and small children.

Drugs that impair kidney function may increase BUN levels. Your BUN and creatinine may be monitored if you are on certain drugs.