The plasma D-dimer assay has been used, along with clinical prediction scores, to rule out pulmonary embolism (PE) in critically ill patients for decades, but a new study suggests it may not be the right test to use in hospitalized COVID-19 patients.
The results showed that all hospitalized patients with COVID-19 and radiographic evidence of PE had plasma D-dimer levels of 0.05 mcg/mL or greater, the cutoff point for the diagnosis.
“If using D-dimer to exclude patients with PE, the increased values we found among 92.3% of patients suggest that this assay would be less useful than in the populations in which it was originally validated, among which a minority of patients had increased D-dimer values,” the authors write. “Setting higher D-dimer thresholds was associated with improved specificity at the cost of an increased false-negative rate that could be associated with an unacceptable patient safety risk.”
The inclusion of patients with D-dimer and computed tomography pulmonary angiography (CTPA) was necessary to estimate diagnostic performance, they note, but “this may have introduced selection bias by excluding patients unable to undergo CTPA.”
“Nonetheless, given the high pretest probability of PE and low specificity observed in this and other studies, these results suggest that use of D-dimer levels to exclude PE among patients hospitalized with COVID-19 may be inappropriate and have limited clinical utility,” they conclude.
Led by Constantine N. Logothetis, MD, from Morsani College of Medicine, University of South Florida, Tampa, the study was published online Oct. 8 as a Research Letter in JAMA Network Open.
Uncertain utility
The authors note that the availability of D-dimer samples routinely collected from hospitalized COVID-19 patients – as well as the heterogeneity of early, smaller studies – generated uncertainty about the utility of this assay.
This uncertainty prompted them to test the diagnostic accuracy of the D-dimer assay among a sample of 1,541 patients who were hospitalized with COVID-19 at their institution between January 2020 and February 2021 for a possible PE.
They compared plasma D-dimer concentrations with CTPA, the criterion standard for diagnosing PE, in 287 of those patients.
Overall, 118 patients (41.1%) required care in the ICU, and 27 patients (9.4%) died during hospitalization.
The investigators looked at the ability of plasma D-dimer levels collected on the same day as CTPA to diagnose PE.
Thirty-seven patients (12.9%) had radiographic evidence of PE, and 250 patients (87.1%) did not.
Overall, the vast majority of patients (92.3%; n = 265 patients) had plasma D-dimer levels of 0.05 mcg/mL or more, including all patients with PE and 225 of 250 patients without PE (91.2%).
The median D-dimer values were 1.0 mcg/mL for 250 patients without PE and 6.1 mcg/mL for 37 patients with PE.
D-dimer values ranged from 0.2 mcg/mL to 128 mcg/mL among patients without PE, and from 0.5 mcg/mL to more than 10,000 mcg/mL among patients with PE. Patients without PE had statistically significantly decreased mean D-dimer values (8.7 mcg/mL vs. 1.2 mcg/mL; P < .001).
A D-dimer concentration of 0.05 mcg/mL was associated with a sensitivity of 100%, specificity of 8.8%, negative predictive value (NPV) of 100%, positive predictive value (PPV) of 13.9%, and a negative likelihood ratio (NLR) of less than 0.1.
The age-adjusted threshold was associated with a sensitivity of 94.6%, specificity of 22.8%, NPV of 96.6%, PPV of 13.9%, and NLR of 0.24.
The authors note that all hospitalized patients with COVID-19 and radiographic evidence of PE had plasma D-dimer levels of 0.05 mcg/mL or greater.