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
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