Simplify d-Dimer Assay for Pulmonary Embolism

Abstract

We read with interest the article by Kline and coworkers1Kline JA Runyon MS Webb WB et al.Prospective study of the diagnostic accuracy of the Simplify D-dimer assay for pulmonary embolism in emergency department patients..Chest. 2006; 129: 1417-1423Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar(June 2006) regarding the diagnostic performance of the Simplify D-dimer assay (Agen Biomedical; Brisbane, Australia) for pulmonary embolism.1Kline JA Runyon MS Webb WB et al.Prospective study of the diagnostic accuracy of the Simplify D-dimer assay for pulmonary embolism in emergency department patients..Chest. 2006; 129: 1417-1423Abstract Full Text Full Text PDF PubMed Scopus (54) Google ScholarThe authors enrolled 2,302 emergency department patients and concluded that such a d-dimer could exclude this diagnosis with a posttest clinical probability of < 1% only in patients with a very low pretest clinical probability. We agree with the authors that the diagnostic performance of the qualitative Simplify D-dimer, as expressed with a negative likelihood ratio of 0.27, is inferior to quantitative enzyme-linked immunosorbent d-dimer assays, which have been recently validated in a metaanalysis with a negative likelihood ratio of 0.08 (95% confidence interval, 0.04 to 0.18), allowing ruling out pulmonary embolism in all patients with low or moderate clinical pretest probability.2Roy PM Colombet I Durieux P et al.Systematic review and meta-analysis of strategies for the diagnosis of suspected pulmonary embolism..BMJ. 2005; 331: 259-263Crossref PubMed Scopus (227) Google Scholar But another disadvantage for the qualitative Simplify D-dimer, which has not been emphasized in the article, concerns its potential influence on the study population itself. Indeed, the low mean age of 44 years as well as the low rate of comorbid clinical conditions in the studied population do not match with the real situation of patients presenting a pulmonary embolism, as it has been evaluated by Aujesky et al3Aujesky D Obrosky DS Stone RA et al.Derivation and validation of a prognostic model for pulmonary embolism..Am J Respir Crit Care Med. 2005; 172: 1041-1046Crossref PubMed Scopus (825) Google Scholarfrom > 10,000 embolic cases. Moreover, the very low prevalence of pulmonary embolism in the study (4.7%), the 99% rate of patients with low or intermediate clinical probability, as well as the 70% rate of negative d-dimer results, do not correspond to previously published outpatient populations.4Perrier A Roy PM Sanchez O et al.Multidetector-row computed tomography in suspected pulmonary embolism..N Engl J Med. 2005; 352: 1760-1768Crossref PubMed Scopus (555) Google ScholarWe therefore suspect that this extremely low threshold for suspecting pulmonary embolism and ordering a d-dimer test is the consequence of using a “too” fast, easy, and cheap d-dimer assay, leading to excessive and inappropriate prescriptions, as it has been previously suggested, but to a lesser extent, even with enzyme-linked immunosorbent d-dimers.5Verschuren F Hainaut P Thys F et al.ELISA d-dimer measurement for the clinical suspicion of pulmonary embolism in the emergency department: one-year observational study of the safety profile and physician's prescription..Acta Clin Belg. 2003; 58: 233-240Crossref Scopus (14) Google ScholarToo much feasibility may decrease efficiency. ResponseCHESTVol. 131Issue 2PreviewThe authors appreciate the thoughtful letter by Dr. Verschuren. We acknowledge here, again, that the Simplify test (Agen; Brisbane, QLD, Australia) can safely rule out pulmonary embolism (PE) only in very low-risk patients. Dr. Vershuren's main worry appears to focus on the young age of our cohort and the low prevalence of PE in it, citing work by Aujesky et al1for comparison. The work by Aujesky et al1was a retrospective, risk-stratification analysis of patients in the Pennsylvania Health Counsel database who had a International Classification of Diseases, ninth revision, discharge code indicating the diagnosis of PE. Full-Text PDF