serum lactate dehydrogenase

Lactate dehydrogenase (LDH or LD) is one of the important enzymes in sugar anaerobic glycolysis and gluconeogenesis. It can catalyze the reduction and oxidation reaction between pyruvic acid and L-lactic acid, and can also catalyze the related α-ketone. acid. LDH is widely distributed in human tissues, with the highest content of heart, kidney and skeletal muscles, followed by liver, spleen, pancreas and lung tissue. The activity of LDH in these tissues is much higher than in serum. Therefore, when a small amount of tissue necrosis, the enzyme releases blood and increases the vitality in other blood. This enzyme is commonly used for the auxiliary diagnosis of myocardial infarction, liver disease and certain malignant tumors. The LDH measurement methods mainly include colorimetry and continuous monitoring. Basic Information Specialist classification: cardiovascular examination classification: biochemical examination Applicable gender: whether men and women apply fasting: fasting Analysis results: Below normal: Reduced by X-ray exposure. Normal value: Enzyme rate method (37 ° C): 218-458 U / L Colorimetric method: 225-540U/L Lactic acid method (37 ° C): 109-245 U / L Pyruvic acid method (3:240-460U/L Above normal: Increased lactate dehydrogenase activity can be used as a useful indicator for the diagnosis of myocardial infarction. LDH began to increase 12-48 hours after myocardial infarction, peaked in 2-4 days, and returned to normal in 8-9 days. Hepatitis, pulmonary infarction, malignant tumors, etc. can also increase LDH. The LDH in the thoracic and ascites caused by tumor metastasis is also often elevated. negative: Positive: Tips: Pay attention to rest before checking, check the need for an empty stomach in the morning. Normal value (1) enzyme rate method (37 ° C) 218 ​​~ 458U / L; (2) colorimetric method 225 ~ 540U / L; (3) lactic acid method (37 ° C) LDH-L109 ~ 245U / L; (4) Pyruvic acid method (37 ° C) LDH-P240 ~ 460U / L. Clinical significance LDH assays are commonly used to diagnose myocardial infarction, liver disease, and certain malignancies. (1) Myocardial infarction. The onset of disease increased from 10 to 12 hours, peaked at 24 to 48 hours, and returned to normal after 8 to 9 days. Compared with CK, although the enzyme activity appeared later, the positive rate is lower, but the duration is long, and the degree of activity is closely related to the condition of myocardial infarction. The larger the infarct size, the higher the enzyme activity. If the recovery of LDH is slow, or increase again during the course of the disease, it indicates that the infarct size is enlarged and the prognosis is poor. (2) Liver disease. Acute or chronic active hepatitis LDH is often markedly or moderately elevated. Its sensitivity is slightly lower than ALT. The LDH activity was significantly increased in liver cancer, especially in metastatic liver cancer. Up to 1000U/L. (3) Blood diseases. Leukemia, megaloblastic anemia, malignant lymphoma and other LDH activities are elevated. (4) Others. Malnutrition, striated muscle injury, pancreatitis, pulmonary infarction and other LDH activities are also elevated. (5) Reduced exposure to X-rays. High results may be diseases: acute myocardial infarction, non-Hodgkin's lymphoma, acute superior mesenteric artery infarction, malignant lymphoma, myasthenia gravis, eyelid non-Hodgkin's malignant lymphoma (1) Colorimetric method: 1 potassium lactate, sodium lactate can also be used as LDH substrate, but because it is an aqueous solution, the content is not accurate enough, and improper storage can easily produce keto acids and inhibit the enzymatic reaction. Lithium lactate is solid, stable and easy to weigh. 2 In addition to the diethanolamine buffer, Tris or pyrophosphate buffer can also be used to avoid the inhibition of LDH by the glycine buffer in the original Jinshi method, and the positive detection rate is improved. 3 colorimetry should be completed within 5 to 15 minutes, otherwise the absorbance will decrease. 4 Results> 2500 U, the specimen can be diluted with physiological saline and then measured, and the result is multiplied by the dilution factor. (2) Continuous monitoring method: 1 specimens do not hemolyze, when hemolysis reaches Hb0.8g / L, LDH activity can be increased by 58%. 2 specimens were stored at room temperature (25 ° C), the enzyme activity was stable within 2 days, the enzyme activity in the refrigerator was decreased, and LDH3 and LDH4 were all inactivated at -20 °C overnight. 3 Satisfactory results with serum or heparin anticoagulated plasma, oxalate can inhibit LDH activity. 4 After the reconstitution, the solution becomes cloudy or the initial absorbance > 0.5 should be discarded. 5 Lactate dehydrogenase activity can be measured by both positive and negative two-way reaction, but the reference interval is also different due to different reaction temperature, substrate and buffer concentration. Using lactic acid and NAD as substrates, the absorbance increase rate was monitored at 340 nm as positive reaction, expressed as LD-L; pyruvate and NADH were used as substrates, and the rate of decrease in absorbance at 340 nm was monitored as reverse reaction, expressed as LD-P. Compared with the two methods of positive and negative reaction, the main advantages of the LD-L method are: A. The stability of the positive reaction substrate liquid is greater than the stability of the reverse reaction. The former refrigerator can be stored for more than 6 months, while the latter is only a few days; The linear range of rate response (absorbance plotted against monitoring time t) is wider; C. repeatability is better than LD-P. Since the reverse reaction rate is faster than the forward reaction rate, its reference value is about twice that of LD-L. Inspection process Immediately after venous blood collection, the test method: (1) Colorimetric method: Mix, place at room temperature for 5 min, at a wavelength of 440 nm, the cuvette light path is 1.0 cm, the distilled water is adjusted to zero point, the absorbance of each tube is read, and the standard curve is checked by the difference of AU-AC to determine the LDH activity unit. (2) Continuous monitoring method: Each laboratory can operate according to the model and instructions of the biochemical automatic instrument. The main parameters are 340nm wavelength, 37 ° C, aspirate sample 500μl, continuous monitoring time 60s, the ratio of sample to reagent volume is 1:50. Not suitable for the crowd Generally no taboos. Adverse reactions and risks 1. Infection: Pay attention to aseptic operation when collecting blood, avoid contamination of water and other parts at the blood collection site to avoid local infection. 2, bleeding: after the blood is given a full compression time, especially coagulopathy, bleeding tendency, to avoid local subcutaneous oozing, bruising and swelling.