D-dimer levels below the conventional cut-off point of 500 µg/l combined with a “low/intermediate” or “unlikely” clinical probability can safely rule out the diagnosis in about 30% of patients with suspected pulmonary embolism.
However, the D-dimer concentration increases with age and its specificity for embolism decreases, which makes the test less useful to exclude pulmonary embolism in older patients; the test is able to rule out pulmonary embolism in 60% of patients aged <40 years, but in only 5% of patients aged >80.
A new, age dependent cut-off value was derived and then validated in two independent retrospective datasets from Belgium, France, the Netherlands, and Switzerland. They studied over 5000 patients aged >50 years.
The new D-dimer cut-off value was defined as (patient’s age x 10) µg/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 µg/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.
Potential of an age adjusted D-dimer cut-off value to improve the exclusion of pulmonary embolism in older patients: a retrospective analysis of three large cohorts.

BMJ. 2010 Mar 30;340:c1475