Determination of the D-dimer cutoff level and its application in the diagnosis of venous thromboembolism in psychiatric patients

Abstract

We determined the D-dimer cutoff level and established a new system for diagnosing pulmonary thromboembolism in the early stages. We then evaluated the usefulness of this new system in patients with physical restraints who were admitted to our psychiatric unit. We performed receiver operating characteristic (ROC) analysis for 186 patients with D-dimer levels of ≥0.5μg/ml who underwent echo and/or contrast-enhanced computed tomography (CT) for assessing the presence of venous thromboembolism. We determined that the D-dimer cutoff level was 3.0μg/ml (sensitivity, 91.7%; specificity, 78.2%; false-positive rate, 78.2%) in these patients. Under the new system, when D-dimer levels are above normal and below the cutoff, patients should undergo frequent examination of oxygen saturation by pulse oximetry (SpO₂), not echo or contrast-enhanced CT, as part of routine testing. When patients exhibit a decrease of ≥3% in SpO₂, we recommend contrast-enhanced CT of the chest and lower limbs because these patients have a strong chance of developing pulmonary embolism. On application of the aforementioned criteria recommended by the new system, we found that among 38 patients with physical restraints who exhibited D-dimer levels that were below the cutoff level for 19 months (from September 2010 to March 2012), none developed venous thromboembolism or related complications. Therefore, determination of the D-dimer cutoff level may enable us to diagnose venous thromboembolism more effectively in psychiatric patients.