SAMPLING Parameter
AChE (n = 10) BChE (n = 10)
Coeffi cient of
determination (R²) 0.93
0.98
Table 1. Correlation of results of AChE and BChE activity determination in whole blood samples, using ChE Check Mobile and a reference method.
following menu-driven steps indicated on the touch screen (Fig 2 on previous page):
1. Baseline measurement (blank value) by positioning of the sample cuvettes into the analysis unit
2. Addition of 10 μl (microlitres) blood sample by using a capillary, shaking the sample cuvettes and measuring the hemoglobin content
3. Addition of reagents by positioning the desired, colour-coded lid onto the cuvettes (AChE or BChE) and mixing
4. Photometric determination of AChE or BChE activity
5. Display of results of AChE or BChE activity (normalized to the haemoglobin content of the sample) including result interpretation and further instructions.
Results for validation ChE Check Mobile was classifi ed as IVD (in vitro diagnostic) and a Class I Medical Device according to EU regulations. In order to allow CE labeling, the device had to pass extensive validation testing. Enzymes such as AChE and BChE show temperature-dependent activity.
FIGURE 3: Determination of ruggedness of ChE rapid test IVD results against tempera- ture eff ects; measurement of native and inhibited AChE activities in whole blood samples (n=4, means ± SD).
Parameter Intra-Day variability (n = 91) Inter-Day variability (n = 45; 5 days)
Inter-Operator variability (n = 30) by measurement of 10 samples by 3 persons)
Coeffi cient of variation (CV) (%) AChE 1.3
1.3 1.7
BChE ▸ 4.5 ▸ 3.3
▸ 5.9
Table 2. Reproducibility of AChE and BChE activity determination in whole blood samples using ChE Check Mobile.
Therefore, an important prerequisite to assure ChE Check Mobile will perform well under fi eld conditions is its ability to function in a wide range of temperatures and to normalize values to 37°C. Accord- ingly, the device contains a temperature sensor to determine the actual assay temperature and a mathematical algorithm to normalize temperature eff ects. Fig. 3 shows examples of AChE
activities determined in native and OP inhibited samples at diff erent tempera- tures showing that determination of AChE and BChE activity at temperatures from 10°C to 50°C is possible. In order to use ChE Check Mobile
for laboratory diagnosis of exposure to AChE/BChE inhibitors, the device needs to provide precise and accurate data on AChE and BChE activity over a wide range. Determination of AChE and BChE activity in whole blood samples with very diff erent enzyme activities in fact confi rmed a linear correlation in a range from minimal to above-average physi- ological values, as shown in Fig. 4. Another part of the validation was the comparison of ChE Check Mobile with a reference method – a modifi ed Ellmann method established at the Bundeswehr Institute of Pharmacology and Toxicology and accredited under DIN EN ISO 15189. Determination of variations of AChE and
BChE activities with both methods demonstrated correlations that, with regard to biological samples, can be considered excellent (correlation of both methods: R² > 0.9; Table 1). In addition, the reproducibility of the device (intra- day variability, inter-day variability and inter-operator variability) was shown to be below 5% (Table 2). Further measurements were done
using real samples from OP pesticide- poisoned patients. As shown in Fig. 5, a good correlation between the ChE Check Mobile and the reference laboratory method is evident, proving the functionality of the device for fi eld applications. ❚❙
FIGURE 4: Linear correlation of AChE values determined by ChE rapid test IVD in blood samples with diff erent (known) AChE activities (n = 4, Means ± SD).
FIGURE 5
Dr. Dipl. Biol. Sebastian Klaus is Head of R&D at Securetec Detektions-Systeme AG, Brunnthal, Germany and as a biologist has over seven years’ experience in developing rapid on-site tests. Dipl. Ing. (FH) Marion Nies is a Project Leader at Securetec with more than 10 years’ experience in project management. The authors thank Dr. Worek and his team for their kind collaboration and the project was funded by the German Ministry of Defence, contract number E/UR3G/8G141/8A800.
34 CBNW 2013/01
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