The creatinine clearance test refers to blood and urine tests that are used to assess kidney function. If the physician determines that a patient may have a kidney function abnormality, such as kidney failure or kidney obstruction, he may recommend a creatinine clearance test. This diagnostic medical test requires both a blood sample and a urine sample. The lab compares the creatinine level in both samples to calculate the clearance rate. Commonly, the patient's height and weight also are taken into account when calculating test results.
Creatinine is produced in the muscles and is a waste product. Typically, creatinine is removed by the kidneys, therefore, elevated levels of this waste product in the bloodstream is an indicator of less than optimal kidney filtration. Generally, the creatinine clearance test measures creatinine levels in the urine and blood that has been manufactured in the last 24 hour time period. These results are used to determine the levels of creatinine that have been cleared out of the blood and filtered into the urine.
Symptoms that may alert the physician to order a creatinine clearance test include facial, abdominal or extremity swelling. In addition, decreased levels of urinary output and bloody, dark or foamy urine are important indicators that a creatinine clearance test may be warranted. Sometimes, flank or mid back pain and the presence of high blood pressure or protein in the urine may alert the physician to order a creatinine clearance test. Typically, there is no special preparation for the test on the part of the patient.
Generally, diseases or conditions that impair the ability of the kidneys to clear waste products from the blood will yield elevated creatinine levels in the blood. In addition, the creatinine clearance value can decrease because decreased amounts of creatinine are excreted through the urine. Sometimes, decreased values of creatinine clearance may indicate congestive heart failure, acute kidney failure, or kidney tumor. Occasionally, elevated values may indicate pregnancy or may be the result of vigorous exercise.
Sometimes, if the patient consumes a diet high in protein or meat, the test will be elevated and warrant a repeat. In addition, certain medications may alter the test. Medications called diuretics may give a false positive reading. Diuretic medications are also known as water pills. These medications promote frequent urination and are indicated in the treatment of hypertension, or high blood pressure. Other medications that may skew test results are stomach acid reducers and certain antibiotics.