• Renée A Douma, Grégoire le Gal, Maaike Söhne, Marc Righini, Pieter W Kamphuisen, Arnaud Perrier, Marieke J H A Kruip, Henri Bounameaux, Harry R Büller, and Pierre-Marie Roy.
• Department of Vascular Medicine, Academic Medical Centre, Meibergdreef 9, 1105 AZ, Amsterdam, Netherlands. R.A.Douma@amc.uva.nl
• BMJ. 2010 Jan 1;340:c1475.

ObjectivesIn older patients, the the D-dimer test for pulmonary embolism has reduced specificity and is therefore less useful. In this study a new, age dependent cut-off value for the test was devised and its usefulness with older patients assessed.DesignRetrospective multicentre cohort study.SettingGeneral and teaching hospitals in Belgium, France, the Netherlands, and Switzerland. Patients 5132 consecutive patients with clinically suspected pulmonary embolism.InterventionDevelopment of a new D-dimer cut-off point in patients aged >50 years in a derivation set (data from two multicentre cohort studies), based on receiver operating characteristics (ROC) curves. This cut-off value was then validated with two independent validation datasets.Main Outcome MeasuresThe proportion of patients in the validation cohorts with a negative D-dimer test, the proportion in whom pulmonary embolism could be excluded, and the false negative rates.ResultsThe new D-dimer cut-off value was defined as (patient's agex10) microg/l in patients aged >50. In 1331 patients in the derivation set with an "unlikely" score from clinical probability assessment, pulmonary embolism could be excluded in 42% with the new cut-off value versus 36% with the old cut-off value (<500 microg/l). In the two validation sets, the increase in the proportion of patients with a D-dimer below the new cut-off value compared with the old value was 5% and 6%. This absolute increase was largest among patients aged >70 years, ranging from 13% to 16% in the three datasets. The failure rates (all ages) were 0.2% (95% CI 0% to 1.0%) in the derivation set and 0.6% (0.3% to 1.3%) and 0.3% (0.1% to 1.1%) in the two validation sets.ConclusionsThe age adjusted D-dimer cut-off point, combined with clinical probability, greatly increased the proportion of older patients in whom pulmonary embolism could be safely excluded.

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