Serum Creatinine and Kidney Failure

Creatinine is one of the indexes during renal function test. 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.
Decreased creatinine levels may be seen in: the elderly, persons with small stature, decreased muscle mass, or inadequate dietary protein. Muscle atrophy can also result in decreased serum creatinine level. If muscle atrophy is suspected, assessment of serum creatine, an important enzyme necessary for normal muscle function, is done.
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.
Increased serum creatinine levels are seen in: Impaired renal function, Chronic Nphritis, Urinary tract obstruction, Muscle diseases such as gigantism, acromegaly, and myasthenia gravis, Congestive heart failure, and shock.