Analysis of inaccurate reasons for biochemical analyzer enzyme test

In the biochemical analysis measurement, the enzyme measurement is more complicated, the requirements are higher, and the test is more difficult. As long as the enzyme is accurate and reproducible, the biochemical analyzer generally has no problem in the determination of other items. Now, some common reasons for inaccurate testing and poor reproducibility in biochemical analyzer enzyme analysis are analyzed for users and maintenance engineers.

Biochemical analyzer enzymes are generally tested by kinetic methods. The principle is to use physical, chemical or enzymatic reaction analysis methods under the optimum conditions of the enzyme reaction, at a constant reaction rate and the activity of the analyte or The concentration is proportional. There are two calculation methods:

1) Absolute law:

Enzyme activity (U/L) = ΔA × (reaction volume / sample volume) × (1000 / extinction coefficient)

2) Relative law:

(U/L or mmol/L) = [ΔA (measurement) / ΔA (standard)] × viability or concentration of the standard

Therefore, the determination of biochemical analyzer enzymes is related to many conditions. Condition settings, such as: wavelength, temperature, parameters, test methods, delay and test time, liquid absorption, etc. In addition, it is also related to the manufacturer's reagents, sample collection and storage, and timely quality control. It is also very important to clean from one sample to another.

For example, the GPT test generally selects: the wavelength is 340 nm, the measurement time is 20 seconds, the delay time is 40 seconds, the liquid absorption is 350 μl, the temperature is set to 37 ° C, and the reagent blank can be arbitrarily selected.

Therefore, the GPT test results are related to the following points:

1. 340nm is the low end of the wavelength, and the energy is low. At the same time, the 340nm filter is used more and is easy to aging. Therefore, the wavelength drift is not accurate, and the half width change will affect the accuracy and repeatability of the measurement.

2. Dynamic method test has delay time and test time requirement. The delay time is the pre-reaction time in the dynamic method, and the test time is the total time of the test in the dynamic method. The zero-order kinetics method is for a specific time period. When the enzyme reaction is started, the reaction is more complicated, and the heterogeneous reaction is more. It takes a period of delay to enter the stable reaction period. Each reagent manufacturer has strict requirements for these two periods. . Therefore, the dynamic method test generally has a temperature of 37 ° C and a delay time of not less than 15 seconds.

3. For the input of the parameters, the given value should be input according to the reagent requirements. The general reagent manufacturer gives instructions in the kit instructions.

4. Reaction temperature.

5, the test blank should be accurate.

6, the amount of liquid absorption directly affects the cross-contamination and measurement repeatability, it is recommended to test the amount of substances with large pollution should be correspondingly increased. Generally it should be greater than 400μl, and the general item is 500μl.

7. Inaccurate test and poor repeatability From the operation point of view, there are mainly reasons: the instrument itself has bubbles in the cuvette; the light source lamp is aging; the light source voltage is unstable; the 340nm filter performance is deteriorated, the transmittance is small; the wavelength is not Accurate and so on. Generally check whether the liquid path interface is loose and leaking, and replace the light source bulb and 340nm filter to solve. As for the circuit problem, the heating element is damaged and the temperature is not controlled, and the problem can only be solved by the engineer.

In short, there are many factors affecting the accuracy of the determination of enzymes. As long as the operation is carefully carried out, comprehensive analysis of the factors affecting the determination, careful analysis, the problem of enzyme determination is not difficult to solve. According to our experience, as long as the reagents and samples are accurate, properly preserved, and the samples are carefully pretreated, the instruments are often maintained, maintained, and carefully operated, and the problems will be solved by themselves.