The Reply.

We thank Dr Zalmay et al for giving us the opportunity to respond to their concerns. The aim of our study was to examine the diagnoses and outcomes of acute medical patients with an elevated D-dimer. Our results confirm that patients with normal D-dimer levels are unlikely to die within 90 days, and that elevated D-dimer levels are not only associated with an increased risk for venous thromboembolism, but are also associated with infection, cancer, heart failure, and anemia. Our results confirm that D-dimer is a nonspecific test, and therefore, is of little diagnostic value in an unselected patient population, but is of prognostic value. This leads us to speculate, but not conclude, that D-dimer could be used as a prognostic marker. The main concern against routine measurement of D-dimers on every emergency department patient is that it would result in superfluous downstream investigations. However, in an observational trial during the current COVID-19 pandemic, in which a third of Danish emergency departments participated, routine measurement of D-dimers in more than 500,000 visits did not result in increased unnecessary radiological investigations. We, of course, agree with Zalmay et al that the jury is still out on routine use of the D-dimer in acute medical illness, and that large multicenter trials will be needed to prove that routine D-dimer measurement leads to improved outcomes.