Biochemical item detection methodology: endpoint method, rate method, two-point method

When we use a biochemistry instrument, there may be multiple detection methods on the parameters of the biochemistry analyzer, such as the endpoint method, the fixed time method (two-point method), and the continuous monitoring method (rate method), and so on. What are the differences between these testing methods?

Biochemical analyzers are instruments used to test human liver function, kidney function, blood glucose, blood lipids, cardiac enzymes, ions and other items, which are now essential testing equipment for liver, kidney, cardiovascular diseases and other diseases in the clinic. Although there are various testing devices in the clinic nowadays, in which the testing principles and methods are different, their main purpose is for detecting the severity of diseases and the potential risk of related diseases.

In order to better distinguish the different testing methodologies and their items, we will briefly introduce three different methodologies and the items they apply.

(1) Endpoint method

It means that after a period of time (usually a few minutes), the reaction proceeds to completion, so that all the substrate (measured substance) is converted into product, and the absorbance of the reaction solution no longer increases (or decreases), and the degree of increase (or decrease) of absorbance is proportional to the concentration of the measured substance, which is called the endpoint method, which is the most ideal analytical method.

The items that take the endpoint method generally include ALB, TP, GLU, TC, TG, CRE, UA, HDL, and LDL.

(2) Kinetic method (i.e. continuous monitoring method, rate method)

It refers to the measurement of enzyme activity or metabolites by the enzymatic method, the absorbance value of the linear period (equal absorbance difference between every two points) in the time-absorbance curve is selected continuously, and the result is calculated by the change in absorbance value per unit of this linear period.

The detection items of the rate method generally include: ALT, AST, LDH, ALP, GGT, AMY, CK

(3) Fixed time method (two-point method)

It refers to the selection of two measurement points on the time-absorbance curve, these two points are neither the initial absorbance of the reaction, nor the end absorbance, the difference in absorbance between these two points is used for the calculation of the results, sometimes called the two-point method.

The two-point method is generally used for UREA, TBA, CO2

Seamaty's SD1Auto Dry Chemistry Analyzer tests items using all three assay methodologies: endpoint, fixed time (two-point method), and continuous monitoring (rate method). Visit Seamaty to learn more about biochemistry analyzers.