Abstract: We identified seven RCTs (1728 participants) evaluating prolonged thromboprophylaxis with LMWH compared with in-hospital thromoprophylaxis followed by placebo or no thromboprophylaxis after discharge. The searches resulted in 1632 studies, of which we excluded 1528. One hundred and four abstracts, eligible for inclusion, were assessed of which seven studies met the inclusion criteria. For the primary outcome, the incidence of overall VTE after major abdominal or pelvic surgery was 13.2% in the control group compared to 5.3% in the patients receiving out-of-hospital LMWH (Mantel Haentzel (M-H) odds ratio (OR) 0.38, 95% confidence interval (CI) 0.26 to 0.54; I2 = 28%; moderate-quality evidence). For the secondary outcome of all DVT, seven studies, n = 1728, showed prolonged thromboprophylaxis with LMWH to be associated with a statistically significant reduction in the incidence of all DVT (M-H OR 0.39, 95% CI 0.27 to 0.55; I2 = 28%; moderate-quality evidence). We found a similar reduction when analysis was limited to incidence in proximal DVT (M-H OR 0.22, 95% CI 0.10 to 0.47; I2 = 0%; moderate-quality evidence). The incidence of symptomatic VTE was also reduced from 1.0% in the control group to 0.1% in patients receiving prolonged thromboprophylaxis, which approached significance (M-H OR 0.30, 95% CI 0.08 to 1.11; I2 = 0%; moderate-quality evidence). No difference in the incidence of bleeding between the control and LMWH group was found, 2.8% and 3.4%, respectively (M-H OR 1.10, 95% CI 0.67 to 1.81; I2 = 0%; moderate-quality evidence). No difference in mortality between the control and LMWH group was found, 3.8% and 3.9%, respectively (M-H OR 1.15, 95% CI 0.72 to 1.84; moderate-quality evidence). Estimates of heterogeneity ranged between 0% and 28% depending on the analysis, suggesting low or unimportant heterogeneity. Prolonged thromboprophylaxis with LMWH significantly reduces the risk of VTE compared to thromboprophylaxis during hospital admittance only, without increasing bleeding complications or mortality after major abdominal or pelvic surgery. This finding also holds true for DVT alone, and for both proximal and symptomatic DVT. The quality of the evidence is moderate and provides moderate support for routine use of prolonged thromboprophylaxis. Given the low heterogeneity between studies and the consistent and moderate evidence of a decrease in risk for VTE, our findings suggest that additional studies may help refine the degree of risk reduction but would be unlikely to significantly influence these findings. This updated review provides additional evidence and supports the previous results reported in the 2009 review.

Plain-language summary: Seven studies were found that addressed this question, including a total of 1728 patients. Continuing blood thinning injections after hospital discharge decreased the risk of both blood clots in the limbs and in the lungs. This review determined that the overall incidence of having a blood clot is reduced from 13.2%, when no post-discharge blood thinner injections are used, to 5.3% when a blood thinner injection is prescribed for at least 14 days following discharge in 30 days follow-up. Both symptomatic and asymptomatic blood clots decreased with the use of prolonged duration blood thinner injections in postoperative patients. No increase in bleeding complications or death, common concerns when blood thinners are used, were observed in patients treated with prolonged duration blood thinner injections. Continuation of blood thinning injections for at least 14 days after abdominal or pelvic surgery reduces the risk of blood clots.