Distinct age-adjusted D-dimer threshold to rule out acute pulmonary embolism in outpatients and inpatients

The diagnosis of acute pulmonary embolism (PE) is combinations of clinical probability assessments, plasma D-dimer (DD) test results, and/or computed tomographic pulmonary angiography (CTPA).

The aim of this study is to explore the appropriate DD cutoff using the immunoturbidimetric method in outpatients and inpatients.

We retrospectively enrolled 2689 patients with suspected PE between January 2014 and December 2019. All patients underwent clinical probability assessments, DD tests, and CTPA. We investigated the appropriate cutoff level for plasma DD tests in the correlation analysis and receiver operating characteristic (ROC) curves.

Among all patients, 1263 were confirmed acute PE. The age-adjusted DD level was determined to be age × 10 μg/L (for patients aged >50 years) in outpatients. This cutoff value resulted in a sensitivity of 96.75% and a specificity of 87.02%, with the area under the curve (AUC) of 0.908 and the number needed to treat (NNT) of 1.18. For inpatients, the age-adjusted cutoff values for the biomarker DD demonstrated poor specificity (13.34%) and NNT (9.88). However, when the DD cutoff was adjusted to 2 × the upper limit of normal (ULN), the sensitivity increased to 93.19%, while the specificity remained at 29.55%, with the AUC of 0.610 and the NNT of 4.76. The optimal DD cut-off value was 3010 μg/L (about 5 × ULN), resulting in a sensitivity of 75.22% and specificity of 61.72%, with the AUC of 0.727 and the NNT of 2.7.

Using the immunoturbidimetric method to measure DD, an age-adjusted DD cutoff (age × 10 μg/L, if aged >50 years) should be considered for outpatients with suspected PE. For inpatients, increasing the DD cutoff value to at least 2 × ULN yields the best test performance.