Comparison of the AQT90 FLEX and Mini Vidas

Report
Comparison of the AQT90 FLEX and Mini Vidas Assays in the D-dimer
Analysis for the Determination of Vascular Traumatic Events
E.N. Shea, A.H. Wu, S. Tu, A. Wong UCSF, San Francisco, Ca
Abstract
Demographics
Methods
Objective: D-dimer, a protein fragment remaining after the degradation of a blood clot,
can be measured in the blood to determine the likelihood of a vascular traumatic
event. Most commonly the test is used to rule out deep vein thrombosis and
pulmonary embolisms. From a diagnostic standpoint these VTEs can share the same
symptoms (shortness of breath, chest pain, and leg swelling) as a host of other
medical problems so it is imperative to rule out a thrombosis as soon as possible.
Point-of care devices shorten the turn around time for blood test results and therefore
prove valuable in an emergent situation. Our study measured D-dimer levels on the
AQT90 FLEX (Radiometer Medical ApS), a point-of-care device against the mini Vidas
(bioMérieux, Inc), used in the clinical laboratory to determine the degree of correlation
between the two assays.
Methods: Data was collected from 116 unique individuals enrolled at UCSF. Of the
subjects, 12 were diagnosed with PEs and one with a DVT. The plasma samples were
collected on sodium citrate and were obtained frozen from the clinical labs after being
used for clinical testing. The samples were defrosted and tested in batches on the
AQT90 FLEX and mini Vidas within 2 hours of each other. Subjects who were not
diagnosed at time of enrollment with a VTE were then contacted 30 days later to
determine if any new thrombosis had occurred.
Results: The subjects consisted of men (n=49) and women (n=67) with a mean age of
51.1 years (SD=17.1). Their ethnicities were covered in five groups; White(n=40),
Black(n=31), Asian(n=12), Hispanic(n=8) and Other(n=16). Well’s scores captured for
51 subjects included Low(n=30), Moderate(n=19) and High(n=2), although none of the
VTEs received a Well’s score. Of the 103 patients who did not have a VTE, 89 were
contacted and none had thromboses at the 30 day follow up point. One patient expired
due to unrelated causes and another suffered a PE several months later. The clinical
comparison show that there was concordance between the two assays with all but four
results in respect to positive and negative tests. The AQT correctly identified a PE as
positive and two subjects as negative that the Vidas reported to the contrary. The AQT
also reported one false positive that the Vidas did not. The remaining 11 VTEs were
identified as positive on both assays.
Discussion: Comparing D-dimer assays is challenging. First of all a comparison
should be primarily a clinical comparison because the specificities for D-dimer assays
can be in the range from 30-90 %. As the number of false-positives is equal to 100 %
minus specificity, it can be seen that a relatively high number of false-positives seems
to be accepted. The main reason for this is that a D-dimer test is used for ruling out
VTE in low-risk patients and that patients with a positive test are examined with a
confirmatory method (imaging).
The challenges come from the fact that D-dimer is not a standardized method. There
exists no reference method and there are no international standards available.
Furthermore, the D-dimer molecules belong to a heterogeneous group of molecules.
This means that it should be known which method was used to interpret a result, and
you cannot directly compare two results obtained with different methods.
Conclusion: There is a strong concordance between the AQT90 Flex results and the
predicate Vidas assay. As D-dimer is used as a rule out test, done before confirmatory
imaging, the AQT provides accurate results from a point-of-care location to help health
care providers make time sensitive diagnoses.
Gender:
•The project was funded by Radiometer Medical ApS who wanted
to evaluate their AQT90 Flex, a multiplatform point-of-care
analyzer, against the FDA approved mini Vidas.
Men (n=49) and Women (n=67)
Age:
•116 unique patients enrolled at UCSF
Mean Age= 51.1 (SD=17.1)
•Sodium citrate plasma was tested from patients in the ED
suspected of having a VTE
Ethnicity:
•Left over samples were obtained frozen after being tested in the
clinical lab
White (n=40), Black (n=31), Asian (n=12), Hispanic (n=8),
•Testing on the AQT90 FLEX and mini Vidas were done within 2
hours of each other
VTE Breakdown:
Other (n=16)
Pulmonary Embolism = 12
Deep Vein Thrombosis = 1
Results
Negative VTE =103
Regression Analysis of the AQT90 FLEX and mini Vidas
Low =30
Wells Score:
Medium =12
High =2
*Wells scores were obtained from 51 of the 116 patients
Results above 5000ng/mL removed as these values are outside of measurable range
while any result above 500ng/ML is considered a positive test
•Results were in concordance with all but four results between
assays
Conclusion
•AQT90 identified a PE as positive and two patients as
negative that the mini Vidas failed to accurately report
The AQT 90 FLEX provides comparable results to the
predicate, mini Vidas. Having a point-of-care D-dimer
assay would allow doctors to rule out time sensitive
diagnosis more quickly.
•AQT90 reported one false positive that the mini Vidas did not
Place closed
tube inside of
device when
prompted by
screen
Select
parameters for
the sample from
the touch
screen
Reload
machine with
next sample
and wait for
results to print

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