Lactic Dehydrogenase (LDH) (T523) [Back]
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| RISK ASSESSMENT VALUE: |
Because LDH is present in almost all body tissues, cellular damage causes an elevation of total serum LDH, thus limiting the diagnostic usefulness of LDH. However, five tissue-specific isoenzymes can be identified and measured using heat inactivation or electrophoresis; two of these isoenzymes, LDH1 and LDH2 appear primarily in the heart, red blood cells, (RBC's), and kidneys; LDH3 primarily in the lungs; and LDH4 and LDH5, in the liver and the skeletal muscles. The specificity of LDH isoenzymes and their distribution pattern are useful in diagnosing hepatic, pulmonary, and erythrocytic damage. But their widest clinical application (with other cardiac enzyme tests) is in diagnosing acute MI. LDH isoenzyme assay is also useful when CPK has not been measured within 24 hours of an acute MI. The myocardial LDH level rises later than CPK (12 to 48 hours after infarction begins), peaks in 2 to 5 days, and drops to normal in 7 to 20 days, if tissue necrosis does not persist. Specifically, in acute MI, the concentration of LDH1 is greater then LDH2 within 12 to 48 hours after onset of symptoms. This reversal of normal isoenzyme patterns is typical of myocardial damage and is referred to as "flipped LDH".
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| NORMAL RESULTS: |
Total LDH levels range from 30 to 115 IU/liter. Distribution is as follows:
LDH1: 18.1% to 29% of total
LDH2: 29.4% to 37.5% of total
LDH3: 18.8% to 26% of total
LDH4: 9.2% to 16.5% of total
LDH5: 5.3% to 13.4% of total.
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| ABNORMAL RESULTS: |
As LDH is present in most body tissues, cellular damage causes an elevation of total serum LDH, thus limiting the diagnostic usefulness of LDH. The five tissue-specific isoenzymes can be identified through electrophoretic separation to help target the site affected:
LDH1 and LDH2 - heart, red blood cells and kidneys
LDH3 - lungs
LDH4 and LDH5 - liver and skeletal muscles
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| ADDITIONAL TESTS: |
Electrophoretic separation of isoenzymes (heart, muscle, and bone/white cells.
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| SAMPLE NEEDED: |
Separated serum from a red-stopper 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: |
The rate of p-nitrophenol liberation is proportional to the alkaline phosphatase activity measured spectrophotometrically, Hitachi Modular.
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| INTERFERING FACTORS: |
" Hemolysis due to rough handling of the sample may affect accurate determination of LDH levels, since RBC's contain LDH1.
" For diagnosis of acute MI, failure to draw the sample on schedule may interfere with test results.
" Failure to send the sample to the laboratory immediately, or to keep the sample at room temperature, may influence determination of LDH isoenzyme patterns.
" Recent surgery or pregnancy can cause elevated LDH levels. Chronic hemolysis, caused by prosthetic heart valves, may also increase LDH levels.
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| PURPOSE: |
" To aid in differential diagnosis of myocardial infarction (MI), pulmonary infarction, anemia, and hepatic disease.
" To support creatine phosphokinase (CPK) isoenzyme test results in diagnosing MI, or to provide diagnosis when CPK-MB samples are drawn too late to display elevation.
" To monitor patient response to some forms of chemotherapy.
" To monitor leukemia.
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| PROFILE INCLUDES: |
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| EXPECTED RANGE: |
100 - 242 U/L
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