tear lactate dehydrogenase

LDH (EC 1.1.1.27) and MDH (EC 1.1.1.37) in tears are mainly derived from the corneal epithelium of the eye. Their concentration in tears is about 20 times that of the enzyme in serum. The tear LDH mainly contains the M subunit, with the highest content of LDH5 and LDH4. The MDH isoenzyme of tears can be separated from MDHs and MDHm by electrophoresis of vinegar membrane. The tears of healthy people are mainly MDHs. Basic Information Specialist Category: Ophthalmology Classification: Biochemical examination Applicable gender: whether men and women apply fasting: not fasting Analysis results: Below normal: Bacterial corneal ulcer and keratoconjunctival chemical injury. Normal value: Tears lactate dehydrogenase: 1.29-9.02U/L Above normal: Corneal conjunctival epithelial damage. negative: Positive: Tips: Rub your eyes with your hands, this will cause eye infections, aggravating the condition and affecting the inspection results. Normal value LDH1.29~9.02U/L; LDH isoenzyme LDH10.66 ± 0.51%; MDH activity is 0.25 ~ 2.2U / L; MDH isoenzyme MDHs 80% ~ 98.1%; MDHm>20% is abnormal; LDH/MDH<69 years old is 3.96±0.7; >70 years old 4.55±0.51. Clinical significance Abnormal results In the bacterial corneal ulcer and keratoconjunctival chemical injury, tear LDH and MDH activity decreased. The LDH isoenzyme H/M ratio and MDHm were increased in different degrees, but MDHm could reflect the corneal damage and the degree of lesion. For example, in corneal ulcers and suspected dry keratoconjunctivitis (KCS), MDHm increased and the H/M ratio of tear LDH did not change significantly. The determination of the ratio of LDH isoenzyme and LDH/MDH in tears contributes to the differential diagnosis of trachoma and chronic conjunctivitis. The H/M ratio of LDH in both tears decreased significantly, but in the trachoma, the LDH/MDH ratio of tears did not change, and the M subunit of LDH increased more significantly. Need to check the diagnosis of corneal disease in the population. Low results may be disease: bacterial corneal ulcer precautions Inappropriate people: generally no special population. Taboo before the examination: rubbing your eyes with your hands, this will cause eye infection, aggravating the condition and affecting the inspection effect. Requirements for inspection: Check with the doctor's instructions. Inspection process 1, colorimetric method: (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 improper storage may cause keto acids to inhibit enzymatic reactions. 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) The colorimetric should be completed within 5 to 15 minutes, otherwise the absorbance will decrease. (4) When the result is >500 U, the sample can be diluted with physiological saline and then measured, and the result is multiplied by the dilution factor. 2. Continuous monitoring method: (1) The specimen should not be hemolyzed. When the hemolysis reaches Hb0.8g/L, the 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 varies depending on the 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. Not suitable for the crowd no. Adverse reactions and risks no.

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