What is Creatinine Clearance



Test Description:
Creatinine is the waste product of creatine phosphate, a compound found in the
skeletal muscle tissue. It is excreted entirely by the kidneys. Increased levels of creatinine
indicate a slowing of the glomerular filtration rate. The creatinine clearance
test consists of two components: a 24-hour urine collection and a blood sample.
Conducting both urine and blood testing allows for the comparison of the serum creatinine
level with the amount of creatinine excreted in the urine. This is a more sensitive
indicator of kidney function than serum creatinine alone. The creatinine
clearance normally decreases with aging due to a decline in the glomerular filtration
rate.
Since “clearance” means the amount of blood cleared of creatinine in 1 minute,
a monitoring of the creatinine clearance rate provides valuable information regarding
the progression of renal disease. A minimum creatinine clearance of 10 mL/minute is
necessary to maintain life without the use of hemodialysis or peritoneal dialysis. The
creatinine clearance rate is calculated by the following formula:

Urine creatinine x urine volume
ـــــــــــــــــــــــــــــــــــــــــــــــــــ              =  Creatinine clearance rate (expressed in expressed in
      Creatinine in Serum                           mL /min / 1.73m2 of body surface)

Normal Values

 Female:             85–125 mL/min (0.8–1.2 mL/sec SI units)
Male:                 95–135 mL/min (0.9–1.3 mL/sec SI units)
Pregnancy:        Increased
Elderly:             Decreased
Children:           Decreased


Possible Meanings of Abnormal Values

Increased                                      Decreased

 Exercise                                         Acute tubular necrosis
Pregnancy                                      Congestive heart failure
Dehydration
Glomerulonephritis
Obstruction of renal artery
Polycystic kidney disease
Preeclampsia
Pyelonephritis
Renal malignancy
Renal tuberculosis
Shock

Contributing Factors to Abnormal Values

• Test results may be altered if urine collection is not kept on ice.
• Drugs which may increase creatinine clearance rate: aminoglycosides, anabolic
steroids, androgens, cefoxitin, chlorpromazine, cimetidine, cisplatin, marijuana,
thiazide diuretics, vancomycin.

Interventions/Implications

 Pretest

• Explain 24-hour urine collection procedure to the patient.
• Stress the importance of saving all urine in the 24-hour period. Instruct the patient to
avoid contaminating the urine with toilet paper or feces.
• Explain that a blood sample will also need to be drawn during the period of the urine
collection.
• Instruct the patient to avoid excessive exercise for 8 hours prior to the test.

Procedure

• Although a 2-hour, 6-hour, or 12-hour urine collection can be used, a 24-hour urine collection
is preferred.
• Obtain the proper container from the laboratory.
• Begin the testing period in the morning following the patient’s first voiding, which is
discarded.
• Timing of the 24-hour period begins at the time the first voiding is discarded.
• All urine for the next 24 hours is collected in the container and kept on ice.
• If any urine is accidentally discarded during the 24-hour period, the test must be discontinued
and a new test begun.
• The ending time of the 24-hour collection period should be posted in the patient’s
room.
• A 7-ml blood sample is drawn in a red-top collection tube anytime during the test period,
usually at the beginning of the collection period.
• Gloves are worn throughout the procedure.

Posttest

• Label the urine container and transport it on ice to the laboratory as soon as possible following
the end of the 24-hour collection period.
• Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued
bleeding.
• Label the blood sample and transport it to the laboratory.
• Report abnormal findings to the primary care provider.

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