D-Dimer Interval Likelihood Ratios for Pulmonary Embolism

Abstract

Objective

To estimate D-Dimer interval likelihood ratios (iLRs) for diagnosing pulmonary embolism (PE).

Methods

The authors used pooled patient-level data from five PE diagnostic management studies to estimate iLRs for the eight D-Dimer intervals with boundaries 250, 500, 750, 1000, 1500, 2500, and 5000 ng/mL. Logistic regression was used to fit the data so that an interval increase corresponds to increasing the likelihood ratio by a constant factor.

Results

The iLR for the D-Dimer interval 1000-1499 ng/mL was essentially 1.0 (0.98 with 95% CI 0.82-1.18). In the logistic regression model, the constant between-interval factor was 2.0 (95% CI 1.9 to 2.1). Using these iLR estimates, if the pre-D-Dimer probability of PE is 15%, only a D-Dimer less than 500 ng/mL will result in a post-test probability below 3%; if the pre-test probability is 5%, the threshold for a “negative” D-Dimer is 1000 ng/mL.

Conclusions

A decision strategy based on these approximate iLRs agrees with several published strategies.

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