Utility of the DASH score after unprovoked venous thromboembolism; a single centre study

The optimal duration of anticoagulation after an unprovoked venous thromboembolism (VTE) is unknown. Three tools that predict recurrence for patients with unprovoked VTE exist: the HERDOO2 [Hyperpigmentation, oEdema or Redness in either leg; D-dimer level ≥250 lg/l; Obesity (body mass index ≥30); or Older age (≥65 years)] score, the Vienna prediction model and the DASH score (Rodger et al, 2008; Eichinger et al, 2010; Tosetto et al, 2012). The DASH score comprises the D-dimer 1 month after stopping anticoagulation (score: +2 if positive), age (+1 if ≤50 years), sex (+1 if male) and use of hormonal therapy ( 2) (Tosetto et al, 2012). Annual recurrence rates are 3 1% [95% confidence interval (CI) 2 3–3 9] for a score of ≤1, 6 4% (95% CI 4 8– 7 9) for ≥2 and 12 3% (95% CI 9 9–14 7) for ≥3 (Tosetto et al, 2012). At our institution, a DASH of ≤1 has been used to discourage long-term anticoagulation in patients with unprovoked VTE where the decision is in equipoise. This study aimed to evaluate the VTE recurrence rate of patients with low DASH scores (≤1) treated at our institution. Medical charts of patients seen in the thrombophilia clinic between 1 January 2013 and 31 December 2016 with a first episode of unprovoked (as defined by Tosetto et al, 2012) or hormone-provoked VTE [proximal deep vein thrombosis (DVT) or pulmonary embolism] were reviewed. The censor date was VTE recurrence, death or 12 April 2018 (whichever occurred first). D-dimer testing was performed 1 month after stopping anticoagulation. Patients were tested for antithrombin deficiency (but not routinely other heritable thrombophilias) and antiphospholipid antibodies as these can influence treatment. The primary outcome was recurrent VTE, which was diagnosed when there was objective radiological evidence of a new VTE. Distal DVT was excluded. Statistical analysis was performed using Microsoft Excel 2010 (Microsoft, Redmond, WA, USA); 95% confidence intervals (CIs) were calculated using the exact binomial method. This project was registered with the hospital audit department. Unprovoked VTE was identified in 452 patients; 5 were lost to all follow-up, 145 continued anticoagulation without a DASH, 27 stopped anticoagulation after the initial treatment period without a DASH and 271 had a DASH calculated, whilst 4 patients had a VTE recurrence having stopped anticoagulation to determine a DASH score and subsequently continued anticoagulation long-term. Of the 271 patients with a DASH score, 145 had a score ≤1 and stayed off anticoagulation, 6 had a DASH ≤1 and resumed anticoagulation, 88 had a DASH ≥2 and resumed anticoagulation and 32 had a DASH ≥2 and stayed off anticoagulation (individual treatment was decided on patient factors, such as preference and perceived bleeding risk). For the 145 patients with a DASH score ≤1 that stayed off anticoagulation there were no recurrences during the initial anticoagulant treatment period (characteristics in Table I); mean age was 62 years and 52 4% were male. No group of patients with a DASH ≤1 had a recurrence rate less than 5/100 patient years and of the recurrences, 12 were male and 10 female (Table II). Expert consensus is that if VTE recurrence rate at 1 year is less than 5% or 15% at 5 years then this is acceptably low to withhold anticoagulation (Kearon et al, 2010). Our findings suggest rates above this; however, this threshold is debatable with low dose direct oral anti-coagulants which have a favourable bleeding profile (Agnelli et al, 2013 & Weitz et al, 2017). Patients that had a DASH score ≤1 represented a clinically low risk group (patients that continued anticoagulation without a DASH score had diverse risk factors for recurrence; data not shown), which makes the recurrence rate surprisingly high. In a recent validation of the DASH score, the recurrence rate for patients aged >65 years was >5% annually even with low DASH scores and therefore the relatively old population in our study (average age for DASH ≤1: 62 years) may have affected recurrence rates; however when patients aged >50 and <65 years were examined in our study, recurrence rates were >5/100 patient years (Tosetto et al, 2017). Tosetto et al (2017) also observed that a DASH score of 1 had an annual recurrence rate of 5 3% (95% CI 5 1–5 4) although the annual rates were significantly lower [3 9% (95% CI 3 6–4 2) and 0 5% (95% CI 0 4–0 6)] for scores of 0 and ≤ 1 respectively, but our findings did not replicate this for the sub-group with a score ≤0. It is known that males have higher recurrence rates (the HERDOO2 score does not allow them to stop anticoagulation) but even when they are excluded (DASH ≤0; Table II) the recurrence rate was more than 5/100 patient years (Rodger et al, 2008). The HERDOO2 score has recently been validated and included patients with ‘weakly provoked’ VTE (aside from hormone therapy), which is a lower risk population in terms of VTE recurrence compared to predominantly unprovoked patients in our study (Rodger et al, 2017). Our study has several limitations. It is an audit of the DASH score at our centre rather than a prospective validation study and outcomes were not adjudicated. The patient’s medical charts