Creatinine, serum (T503) [Back]
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| RISK ASSESSMENT VALUE: |
Creatinine is a non-protein end product of creatine (muscle and protein in the diet) metabolism. Similar to creatine, creatinine appears in serum in amounts proportional to the body's muscle mass. Unlike creatine, it is quickly excreted by the kidneys, with minimal or no tubular reabsorption. Creatinine levels, therefore, are directly related to the glomerular filtration rate. Since creatinine levels normally remain constant, elevated levels usually indicate diminished renal function.
Elevations are not usually detectable until one-half of kidney function is destroyed. One healthy kidney is usually sufficient to maintain normal creatinine levels because of hypertrophy (loss of other kidney when young) or simply increased blood flow. Men (larger muscle mass) have slightly higher values than women and individuals with very high muscle mass run to the high end of normal.
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| NORMAL RESULTS: |
0.6 - 1.5 mg/dL (53-133 umol/L)
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| ABNORMAL RESULTS: |
Low values are not of concern and are expected in pregnancy due to increased renal blood flow.
High values may indicate decreased renal function especially in conjunction with high or borderline high BUN values. Once abnormal, small increases in creatinine may represent large changes in glomerular filtration rate (GFR). Marked disparity between the BUN and creatinine relative to expected suggests a sample problem.
Athletes with high muscle mass relative to height may have values at the high end of the range. This may be further affected if they use creatine supplements which are then further metabolized to creatinine potentially leading to slightly abnormal results. Samples delayed in transit may exhibit small increases in creatinine levels as well.
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| ADDITIONAL TESTS: |
Evaluate in conjunction with the BUN value
Creatinine clearance can be quickly estimated using the attached internet link for the Medical College of Wisconsin which also provides the Cockcroft and Gault equation most often used for the estimate: Online Clinical Calculator for Creatinine Clearance.
| Age | Male | Female |
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| 20-39 | 90-140 | 75-120 |
| 40-59 | 70-120 | 50-100 |
| 60-69 | 55-100 | 45-75 |
| 70-79 | 45-80 | 40-65 |
| 80-89 | 30-60 | 30-55 |
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| SAMPLE NEEDED: |
Separated serum from a red-stop tube.
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| SAMPLE STABILITY: |
10 days at room temperature; 2 weeks when refrigerated, indefinitely when frozen.
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| METHOD & INSTRUMENT: |
Creatinine forms a complex with picric acid (Jaffe reaction) with the rate of reaction measured spectrophotometrically, Hitachi Modular.
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| INTERFERING FACTORS: |
None
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| PURPOSE: |
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| PROFILE INCLUDES: |
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| RISK RANGE & UNITS: |
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