Age-adjusted D-dimer cutoff point increased proportion of older patients who could be excluded for pulmonary embolism

A cutoff value adjusted to age along with clinical probability increased the number of patients who could be excluded for pulmonary embolism without reducing safety.

Although the D-dimer test is a valuable diagnostic tool for ruling out pulmonary embolism, its specificity decreases with age, making it less useful.

Researchers, therefore, constructed a new, age-dependent D-dimer cutoff value in patients older than 50 years and analyzed its safety and clinical utility in combination with clinical probability assessment.

The researchers examined data from two prospective studies, including 1,721 outpatients suspected of pulmonary embolism. They then validated the cutoff value with two other large studies: one included 3,306 patients and the other included 1,812 patients.

The new cutoff value was defined as the patient’s age multiplied by 10 mcg/L. For patients in the derivation set with an “unlikely” score (n=1,331), pulmonary embolism could be excluded in 42% of patients with the new cutoff value vs. 36% with the old cutoff value of less than 500 mcg/L.

For the validation sets, there was an increase of 5% for patients with a D-dimer less than the new cutoff value and an increase of 6% for patients with a D-dimer less than the old cutoff value.

The absolute increase ranged from 13% to 16% for the three data sets and was largest among those older than 70 years.

The false-negative rate with the new age-adjusted cutoff value was 0.2% (95% CI, 0-1.0) in the derivation set, 0.6% (95% CI, 0.3-1.3) in the first validation set and 0.3% (95% CI, 0.1-1.1) in the second validation set.

“The next step would be to validate this new D-dimer cutoff value prospectively before implementation in daily practice,” the researchers said.

Douma RA. BMJ. 2010;doi:10.1136/bmj.c1475.