by Gong Xiaolin
Shanghai Center for Clinical Laboratory
When the liver, heart and other organs of the human body are critically damaged, a large quantity of alanine aminotransferase (ALT), aspartate aminotransferase (AST), creatine kinase (CK) and other enzymes will be released, which greatly increases their concentration in the peripheral blood. Under such circumstances, these enzymes’ concentration far exceeds the linear range of reagent. It is very likely that the substrates in the reagent would be consumed very fast, and lead to that the reaction is no longer at zero-order and cause the report results far below actual concentration.
Mindray BS series chemistry analyzers with built-in substrate depletion limit parameters can provide an alarm flag for substrate depletion. When the device detects the depletion of substrate during reaction, it will start the linearity extension function, and use photometric points with linear change in default reaction time (or in lag time) to calculate ∆A/min ratio and report its corresponding results.
The BS-2000M2 automatic biochemical analyzing system is a modular biochemical analyzing device independently developed by Shenzhen Mindray Medical Bioelectronics Co., Ltd. Using BS-2000M2, this study will do a series of routine chemistry tests such as ALT, AST, ALP, GGT, LDH, α-HBDH, CK, CK-MB, α-AMY and UREA tests, all with high-concentration of analytes, so as to give a general assessment on BS-2000M2 about its enzyme linear extension function in clinical practice.
Material and Method
Source of Samples
The research team collected serum samples, from both outpatient and inpatient departments, from the Xuhui Hospital of Fudan Zhongshan Hospital. A total of 63 samples, all with a high concentration of analytes such as ALT, AST, ALP, GGT, LDH, α-HBDH, CK, CK-MB, α-AMY and UREA. The concentration of these analytes falls into three categories: within the linear up-limit, around the linear up-limit and exceeding the linear up-limit. All samples were free of visible hemolysis and lipidemia.
Device and Reagents
BS-2000M2 and the original reagent kits, calibrators and quality control products for testing ALT, AST, ALP, GGT, LDH, α-HBDH, CK, CK-MB, α-AMY and UREA were all purchased from Shenzhen Mindray Medical Bioelectronics Co., Ltd.
First, perform calibration and maintenance of the device according to recommended methods from the manufacturer. Ensure that all testing items are within the effective calibration period and quality control is under control.
The basic principle of enzyme linear extension function is that when the reaction is over, the system will search for the absorbance points with linear change during the reaction time according to substrate depletion limit. If the number of absorbance points with linear change in reaction time (N) is 1 or 0, the system will start linear extension function and find the linear absorbance points without substrate depletion in lag time period, then calculate △A/min of these points and report calculated result (Figure 1). If this calculated result exceeds reagent linearity upper limit, a “>” mark will be given. If the number of absorbance points with linear change in lag time (N) is still 1 or 0, the result cannot be calculated and an "ENC" mark will be given to indicate this error. Then the system will trigger auto-dilution and rerun the sample to report a normal result.
Figure 1: The principle of enzyme linear extension function
The clinical performance of a biochemical analyzer is affected by many factors such as the device itself, reagent performance, integration application protocol, manufacturer s traceability, daily calibration and maintenance in the laboratory etc. When ’ choosing a biochemical analyzer, the laboratory should pay special attention to ensure that the device can do substrate depletion monitoring in kinetic-based tests.
In this study, the linear extension function of BS-2000M2 was proved to be good. The results showed that the upper limits of the reportable range of the ten tests were extended, respectively, to 3339 U/L, 7411 U/L, 3407 U/L, 3945 U/L, 7646 U /L, 9783 U/L, 14106 U/L, 3296 U/L, 9700 U/L and 54 mmol/L (Table 1). It can be inferred that in each test, when the result is lower than the maximum mentioned above, the relative deviation between the calculated result with enzyme linearity extension function and the rerun result after dilution is clinically acceptable. Besides, there is no false alarm or omission of substrate depletion during the research.
|Item||Upper limit of reagent linearity range||Upper limit of reportable range with linear extension function||Highest clinically visible concentration||Sample quantity||Sample proportion within reportable range (%)|
Table1: The reportable range of 10 chemistry items with kinetic reaction method
Figure 2: Inbuilt Index of Substrate Depletion Mark of ALT and Optional Enzyme Linear Extension function in software
In summary, the linear extension function for enzyme parameters on BS-2000M2 greatly extends the reportable range, which effectively reduces the risk of false negative results of high-concentration samples, lowers down the frequency of retesting, and shortens the sample turn-around time
Special appreciation goes to Song Yunxiao from the Department of Laboratory at the Xuhui Hospital of Fudan Zhongshan Hospital for his assistance in collecting the samples for this study.
This article was first published in Laboratory Medicine, Volume 32/9, September 2017.
Original Title: Substrate Depletion Limit Parameters: Role of substrate depletion limit parameters in BS-2000M2 automatic chemistry analysis system
This article is only part of the original text. For the relevant data and complete content, see the original text.