Serum lactate dehydrogenase (LDH)

Lactate dehydrogenase is an important enzyme in the process of energy metabolism in the body. This enzyme is present in almost all tissues, with the most in the liver, kidney, heart muscle, skeletal muscle, pancreas and lungs. 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.

Basic Information

Specialist classification: cardiovascular examination classification: biochemical examination

Applicable gender: whether men and women apply fasting: fasting

Tips: Do not hemolyze the specimen. 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

1, 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.

2, 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.

3. Reduce the exposure to X-rays.

High results may be diseases: pediatric myocarditis, myocardial infarction, pediatric neuroblastoma, liver disease, myotonic dystrophy, myocardial infarction complicated with mitral regurgitation

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

Inappropriate people: Generally there are no people who are not suitable.

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.