Lactate dehydrogenase (LDH or LD) is one of the important enzyme systems of anaerobic glycolysis and gluconeogenesis, which can catalyze the reduction and oxidation reaction between pyruvate and L-lactic acid, and also catalyze relatedα-Ketoacid.LDH widely exists in human tissues, with the highest content in heart, kidney and skeletal muscle, followed by liver, spleen, pancreas and lung tissues.LDH determination methods mainly include colorimetric method and continuous monitoring method.
(1) Colorimetry: 150-450U/L.(2) Continuous monitoring method: male 80-280U/L female 100-230U/L
Clinical significance
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LDH determination is commonly used to diagnose myocardial infarction, liver disease and some malignant tumors.(1) Myocardial infarction: the incidence of myocardial infarction increased 10-12h, peaked 24-48h, and returned to normal 8-9 days later.Compared with CK, although the enzyme activity appeared late and the positive rate was low, it lasted for a long time, and the degree of increase in activity was closely related to the condition of myocardial infarction. The larger the infarct size, the higher its enzyme activity.If LDH recovers slowly after increasing, or increases again during the course of the disease, it indicates that the infarct area is enlarged and the prognosis is poor.(2) Liver disease: LDH in acute hepatitis or chronic active hepatitis is often significantly or moderately elevated.Its sensitivity is slightly lower than ALT.LDH activity increased significantly in HCC, especially in metastatic HCC.Up to 1000U/L.(3) Hematological diseases: leukaemia, megaloblastic anemia, malignant lymphoma and other LDH activities increase.(4) Others: malnutrition, striated muscle injury, pancreatitis, pulmonary infarction and other LDH activities are also increased.
matters needing attention
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(1) Colorimetry: ① Potassium lactate and sodium lactate can also be used as LDH substrates, but because they are aqueous solutions, the content is not accurate enough, and they are easy to produce ketoacids and inhibit enzymatic reaction due to improper storage.Lithium lactate is solid, stable and easy to weigh.② In addition to diethanolamine buffer, Tris or pyrophosphate buffer can also be used to avoid the inhibitory effect of glycine buffer on LDH in the original Ginseng's method, and improve the positive detection rate.③ Colorimetry shall be completed within 5-15min, otherwise the absorbance will decrease.④ When the result is>2500U, the sample can be diluted with normal saline and measured again, and the result is multiplied by the dilution multiple.(2) Continuous monitoring method: ① Do not lyse the sample. When the hemolysis reaches Hb 0.8g/L, the LDH activity can increase by 58%.② The samples were stored at room temperature (25 ℃), and the enzyme activity was stable within 2 days, while the enzyme activity was reduced when stored in the refrigerator. LDH3 and LDH4 were all inactivated when stored at - 20 ℃ overnight.③ Oxalate can inhibit the activity of LDH.④ After re dissolution, the solution becomes turbid or the initial absorbance>0.5 should be discarded.⑤ The activity of lactate dehydrogenase can be measured by both forward and reverse two-way reactions, but the reference range is different due to different reaction temperature, substrate and buffer concentration.With lactic acid and NAD as substrates, the absorbance increase rate monitored at 340nm is a positive reaction, represented by LD-L;Using pyruvic acid and NADH as substrates, monitoring the decline rate of 340nm absorbance is a reverse reaction, expressed as LD-P.Compared with the forward and reverse reaction methods, the main advantages of the LD-L method are: A. The stability of the substrate solution of the forward reaction is greater than that of the reverse reaction. The former can be stored in the refrigerator for more than 6 months, while the latter can only be stored for a few days;B. The linear range of rate reaction (absorbance versus monitoring time t) is wide;C. Repeatability is better than LD-P.Since the reverse reaction speed is faster than the forward reaction speed, its reference value is about twice of LD-L.
Related diseases
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Acute pulmonary heart disease, anemia caused by folic acid deficiency, pediatric glycogen storage disease type II, muscular dystrophy, primary lymphoma, malignant lymphoma of vulva, acute myeloid leukemia, hepatitis C virus infection and glomerulonephritis, progressive muscular dystrophy, myasthenia gravis in the elderly
