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D-dimer levels may predict postoperative VTE
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D-dimer levels higher than 2 mg/L strongly predicted venous thromboembolism in a cohort of patients who underwent elective craniotomy.
Julian Prell, MD, of the department of neurosurgery at the University of Halle in Germany, and colleagues aimed to test the hypothesis that D-dimer levels may become systematically elevated among patients in the postoperative setting. If this hypothesis proved reliable, it may be possible to define a feasible threshold for identifying VTE, according to the researchers.
The study included 101 patients who underwent ultrasound of the lower extremity before and after elective craniotomy. Clinicians assessed D-dimer levels 3, 7 and 10 days after surgery.
Results indicated systematically elevated D-dimer plasma levels among postoperative patients. These levels were significantly different among patients with VTE compared with those who did not have VTE.
Day 3 results demonstrated that D-dimer elevations of more than 2 mg/L indicated VTE with a sensitivity of 95.3% and a specificity of 74.1%. This result allowed for the definition of a feasible threshold, Prell and colleagues wrote.
Among all nine patients with a pulmonary embolism after surgery, D-dimer levels of more than 4 mg/L were reported.
“Using a threshold of 2 mg/L, D-dimer levels will indicate VTE with a high degree of sensitivity and specificity in patients who have undergone craniotomy,” the researchers concluded.
Significant risk factors for VTE included ventilation time and duration of surgery.
“We were honestly surprised by the clarity of our own results, which strongly contradict the established doctrine,” Prell said in a press release. “Before this study, D-dimer plasma levels were considered to be completely unreliable in the postoperative period. Now, screening for venous thromboembolism using D-dimer plasma levels appears to be very straightforward and clinically applicable. We feel that utilizing this method as a routine measure in the perioperative management of neurosurgical patients has great potential to make their surgery safer, and we hope that similar studies will be conducted in other surgical fields.”
Disclosure: The researchers report funding from the Wilhelm Roux Program of Martin Luther University Halle-Wittenberg in Germany.
Perspective
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Adam Cuker, MD, MS, FACP
Measurement of D-dimer is a widely used and highly sensitive test in outpatients with clinically suspected venous thromboembolism (VTE). However, at the standard cut-off of 0.5 mg/L, D-dimer testing is of limited value in postoperative patients because D-dimer levels increase after surgery.
Prell and colleagues conducted a prospective study of 101 patients undergoing elective craniotomy, a population at high thrombotic risk, with the goal of identifying a diagnostic D-dimer threshold. All subjects underwent screening lower extremity ultrasonography 3 to 6 days after surgery, as well as D-dimer measurement at serial time-points. The primary outcome was symptomatic or asymptomatic VTE.
As expected, D-dimer levels rose following surgery. At a cut-off of 0.5 mg/L, the specificity of the D-dimer for VTE on postoperative day 3 was only 38.2%, underscoring its limited utility in the postoperative setting. At a cut-off of 2.0 mg/L, however, specificity improved to 74.1% and sensitivity remained high at 95.3%.
The authors concluded that a D-dimer of 2.0 mg/L may be a useful threshold for identifying VTE after craniotomy. Their results require confirmation in an independent study, ideally with the primary outcome limited to symptomatic VTE. Nevertheless, they suggest the potential value of D-dimer testing after surgery.
In addition to surgery, other factors — including advanced age, cancer and pregnancy — increase D-dimer levels. Recent work has demonstrated the value of age-adjusted D-dimer cut-offs. Identifying useful diagnostic cut-offs for VTE in patients with pregnancy and cancer also may be feasible. It is now apparent that one D-dimer cut-off does not fit all. Rather, cut-offs tailored to the clinical population may expand the applicability of D-dimer testing to a broader range of patients.
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