Comparison of the Simplify D-dimer assay performed at the bedside with a laboratory-based quantitative D-dimer assay for the diagnosis of pulmonary embolism in a low prevalence emergency department population.
BACKGROUND
The immunofiltration D-dimer assay could allow point-of-care testing for pulmonary embolism (PE). A study was undertaken to compare a clinician-performed qualitative D-dimer assay with the automated quantitative D-dimer test.


METHODS
A prospective observational study was conducted from January to October 2005 at an urban academic emergency department (ED). 1193 patients of mean (SD) age 47 (16) years (66% female) were enrolled. The study protocol combined pretest probability estimation, D-dimer testing by both a qualitative immunochromatographic assay (Simplify) performed at the point of care by 192 different clinicians and a quantitative D-dimer test performed in a CLIA-certified laboratory. The criterion standard was image-proven PE or deep venous thrombosis within 45 days after enrollment. To test interobserver agreement for the qualitative assay, two blinded observers independently read 841 Simplify cartridges.


RESULTS
Of 1193 patients enrolled, 45 were PE+ (3.8%, 95% CI 2.8% to 5.0%). Qualitative results were available for 1169 (98%) and quantitative results were available for 1136 (95%). Comparison of the qualitative and quantitative D-dimer tests gave the following results: sensitivity 91% (95% CI 78% to 98%) vs 93% (95% CI 80% to 98%); specificity 57% (95% CI 54% to 60%) vs 57% (95% CI 54% to 60%); likelihood ratio negative 0.16 (95% CI 0.06 to 0.37) vs 0.13 (95% CI 0.05 to 0.35). The weighted Cohen's kappa for interpretation of the qualitative assay was 0.69 (95% CI 0.63 to 0.76).


CONCLUSIONS
In this very low-risk ED population, a qualitative D-dimer assay performed at the point of care had similar diagnostic accuracy to the quantitative D-dimer test. Interobserver agreement for the qualitative test was good.
Runyon
M S
MS
Department of Emergency Medicine, Carolinas Medical Center, PO Box 32861, Charlotte, North Carolina 28323-2861, USA.
Beam
D M
DM
King
M C
MC
Lipford
E H
EH
Kline
J A
JA
D000465:Algorithms; D000792:Angiography; D015331:Cohort Studies; D004636:Emergency Service, Hospital; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009657:North Carolina / Q000453:epidemiology; D019095:Point-of-Care Systems; D015995:Prevalence; D011446:Prospective Studies; D011655:Pulmonary Embolism / Q000097:blood* / Q000000981:diagnostic imaging / Q000453:epidemiology; D012680:Sensitivity and Specificity
D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D