Introduction The determination of von Willebrand Factor cleaving protease ADAMTS13 activity in
plasma is an important diagnostic test to enable the differentiation of patients with
thrombotic thrombocytopenic purpura (TTP) from those with other thrombotic microangiopathies
(TMAs). It is critical to have a reliable ADAMTS13 Activity result within a quick
reporting turn-around time to increase the possibility of a positive outcome of patient
care, especially with TTP patients. The screening test has been described by Moore
et al1. It is a rapid semi quantitative assay requiring no special laboratory equipment
or highly skilled technician to perform the test. The operator determines the ADAMTS13
activity level by comparing the color (red) intensity of the 4 different levels (0,
0.1, 0.4 and 0.8 IU/mL) indicated on the color card verses the test well coloration.
However, on relying in human interpretation from the colour card can potentially lead
to variations in reported results. The aim wasto improve result interpretation by
evaluating a small mobile measuring device to determine the colour intensity of the
screen test. With a digital patient read out of the ADAMTS13 activity level, this
should improve the consistency of result reporting, easy of use and confidence of
patient results with the screening test [1].
Method To test the analytical performance of the measuring device in combination with the
screening test, a three-way method comparison was performed. Patient and normal samples
were assayed in a FRET assay, which was considered as the reference method and a Screening
method with result interpretation using a colour card and a measuring device.
Results The repeatability using the measuring device for low sample and high sample was 2.4
& 0.4% n=10. Determining the colour intensity using the colour card (x3 operators)
vs the measuring device value gave very comparable results. The calculated correlation
betweenFRET vs Screening method/measuring device was r²=0.83. The analytical performance
of the FRET vs Screening method/device was calculated using a cut off value of≤0.1
IU/mL and≤20 respectively, resulting in a specificity of 89% and sensitivity of 79%.
Conclusion Our results showan excellent correlation between all 3 methods, suggesting the mobile
measuring device would be an appropriate and reliable device for determining the ADAMTS13
Activity in the screening test. Therefore, patient results could be reported with
confidence in timely manner aiding the rapid diagnosis TTP patients.
