creatinine, blood (Serum creatinine)
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p307-308
2025-11-29
48
Type of test Blood
Normal findings
* Adult:
- Female: 0.5-1.1 mg/dL or 44-97 μmol/L (SI units)
- Male: 0.6-1.2 mg/dL or 53-106 μmol/L (SI units)
* Elderly: decrease in muscle mass may cause decreased values
* Adolescent: 0.5-1 mg/dL
* Child: 0.3-0.7 mg/dL
* Infant: 0.2-0.4 mg/dL
* Newborn: 0.3-1.2 mg/dL
Possible critical values
> 4 mg/dL (indicates serious impairment in renal function)
Test explanation and related physiology
This test measures the amount of creatinine in the blood. Creatinine is a catabolic product of CPK, which is used in skeletal muscle contraction. The daily production of creatine, and subsequently creatinine, depends on muscle mass, which fluctuates very little. Creatinine, as with BUN, is excreted entirely by the kidneys and therefore is directly proportional to renal excretory function. Besides dehydration, only such renal disorders as glomerulonephritis, pyelonephritis, acute tubular necrosis, and urinary obstruction will cause abnormal elevations in creatinine.
The serum creatinine test, as with BUN, is used to diagnose impaired renal function. The creatinine test is used as an approximation of glomerular filtration rate (GFR). The serum creatinine level has much the same significance as the BUN level but tends to rise later. Therefore elevations in creatinine suggest chronicity of the disease process. In general, a doubling of creatinine suggests a 50% reduction in GFR. The creatinine level is interpreted in conjunction with the BUN test. These tests are referred to as renal function studies. The BUN/creatinine ratio is a good measurement of kidney and liver function. The normal adult range is 6 to 25, with 15.5 being the optimal adult value for this ratio.
Although serum creatinine is the most commonly used bio chemical parameter to estimate GFR in routine practice, there are some shortcomings. Such factors as muscle mass and protein intake can influence serum creatinine, leading to an inaccurate estimation of GFR. On the other hand, cystatin C, a protein that is produced at a constant rate by all nucleated cells, is probably a better indicator of GFR. Because of its constant rate of production, its serum concentration is determined only by glomerular filtration. Its level is not influenced by those factors that affect creatinine and BUN.
Cystatin C might predict the risk for developing chronic kidney disease, thereby signaling a state of preclinical kidney dysfunction. Several studies have found that increased levels of cystatin C are associated with the risk of death and several types of cardiovascular disease. For women, the average reference interval is 0.52 to 0.9 mg/L with a mean of 0.71 mg/L. For men, the average reference interval is 0.56 to 0.98 mg/L with a mean of 0.77 mg/L.
Interfering factors
* Drugs that may increase creatinine values include ACE inhibitors, aminoglycosides, cimetidine, heavy-metal chemotherapeutic agents, and other nephrotoxic drugs.
Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: red
• For pediatric patients, blood is drawn from a heel stick.
Abnormal findings
Increased levels
- Glomerulonephritis
- Pyelonephritis
- Acute tubular necrosis
- Urinary tract obstruction
- Reduced renal blood flow (e.g., shock, dehydration, congestive heart failure, atherosclerosis)
- Diabetic nephropathy
- Nephritis
- Rhabdomyolysis
- Acromegaly
- Gigantism
Decreased levels
- Debilitation
- Decreased muscle mass (e.g., muscular dystrophy, myasthenia gravis)
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