Serum Creatinine Vs Creatinine Clearence

SERUM CREATININE

Measuring serum creatinine is a useful and inexpensive method of evaluating renal dysfunction. Creatinine is a non-protein waste product of creatine phosphate metabolism by skeletal muscle tissue. Creatinine production is continuous and is proportional to muscle mass.

Creatinine is freely filtered and therefore the serum creatinine level depends on the Glomerular Filtration Rate (GFR). Renal dysfunction diminishes the ability to filter creatinine and the serum creatinine rises. If the serum creatinine level doubles, the GFR is considered to have been halved. A threefold increase is considered to reflect a 75% loss of kidney function.

Reference values for serum creatinine:

·       Adult males: 0.8 - 1.4 mg/dl: values are slightly higher in males due to larger muscle mass

·       Adult females: 0.6 - 1.1 mg/dl: creatinine clearance is increased in pregnancy, resulting in lower serum levels

·       Children: 0.2 - 1.0 mg/dl: slight increases with age because values are proportional to body mass

·       A panic value for creatinine is 10 mg/dl in nondialysis patients.

Test results can vary based on a person's size, muscle mass and gender, as well as which laboratory performed the test and which lab method was used. Serum creatinine ranges typical for women are 0.5 to 1.0 milligrams per deciliter. Typical levels for men are 0.7 to 1.2 mg/dl. While a male bodybuilder may have normal kidney function with a serum creatinine level of 2.0 mg/dl, a level of 0.7 mg/dl can indicate significant renal disease in a frail old woman. It is more informative for patients to look at changing levels over time than to rely on a single measurement. A serum creatinine level of 1 mg/dl, for instance, might be considered normal -- unless it is being compared against a recent result of 0.6,which would make it very abnormal.

Increased serum creatinine levels are seen in:

·       Impaired renal function

·       Chronic nephritis

·       Urinary tract obstruction

·       Muscle diseases such as gigantism, acromegaly, and myasthenia gravis

·       Congestive heart failure

·       Shock

The only important pathological condition that causes a significant increase in the serum creatinine level is damage to a large number of nephrons. Unlike the BUN, the serum creatinine level is not affected by hepatic protein metabolism. Tests to measure serum creatinine, urine creatinine, and creatinine clearance are all used only to evaluate renal function. Only renal dysfunction changes the results. The serum creatinine level does not rise until at least half of the kidney's nephrons are destroyed or damaged. Because creatinine levels rise and fall more slowly than BUN levels, creatinine levels are often preferred to monitor renal function on a long-term basis.

CREATININE CLEARENCE

This test measures how well your kidneys remove creatinine from your blood. It gives better information than a serum test on how well your kidneys are working. This test is performed on both a blood sample and on a sample of urine collected over 24 hours.

Normal Result

Creatinine clearance is measured as milliliters/minute (ml/min). The normal values are:

·      Male: 97 to 137 ml/min

·      Female: 88 to 128 ml/min

The normal value ranges may vary slightly from one laboratory to another.

Below Normal Result

A low creatinine clearance might indicate a serious kidney disorder. The kidney damage can either be acute (sudden) or chronic (long-term), which can be identified by repeated tests over time. A lower than normal value may indicate :

·      Life-threatening infection

·      Shock-Cancer

·      Low blood flow to the kidneys

·      Urinary tract blockage

·      Heart failure

·      Dehydration

Cirrhosis