Lactic acid is an intermediate product of glucose metabolism in the body, which is mainly produced by red blood cells, striated muscle and brain tissue. The concentration of lactic acid in the blood mainly depends on the synthesis speed and metabolic rate of liver and kidney. The bidirectional conversion of lactic acid and pyruvate is regulated by lactate dehydrogenase (LDH).

Using NAD+ as H+ receptor, LDH catalyzes the reaction of lactic acid and NAD+ to generate pyruvic acid and NADH respectively. NBT is reduced to a kind of purple compound during the reaction. Measure the OD value at 530 nm, and the concentration of lactic acid can be calculated.

1. Severe hemolysis or jaundice may raise the OD value.

2. If the LA content is calculated by protein concentration, the protein concentration of the sample needs to be determined separately (E-BC-K318-M, E-BC-K168-S, E-BC-K165-S).

1. Blank well: add 0.02 mL of double distilled water into the 5 mL EP tube.

    Standard well: add 0.02 mL of 3 mmol/L lactic acid standard into the 5 mL EP tube.

    Sample well: add 0.02 mL of sample into the 5 mL EP tube.

2.  Add 1.0 mL of enzyme working solution and 0.2 mL of reagent 3 orderly to the tubes.

3.  Mix fully and incubate at 37℃ water bath for 10 min exactly.

4.  Add 2 mL of reagent 4 to the tubes.

5.  Mix thoroughly, set spectrophotometer to zero with double distilled water and measure the absorbance of each tube at 530 nm with 1 cm optical path quartz cuvette.