Seven RCTs (1,379 patients) were included in the review.
In five RCTs randomisation was adequately concealed, while in four of these treatment was not blinded. The outcome assessment was blinded in four RCTs.
Recurrent symptomatic VTE (7 RCTs): LMWH reduced the risk of recurrent symptomatic VTE at 3 months compared with OA, but the reduction was not statistically significant (OR 0.66, 95% CI: 0.41, 1.07). No significant heterogeneity was detected (P=0.12). The meta-analysis had 78% power of detecting a 50% reduction in recurrent symptomatic VTE.
Bleeding (7 RCTs): there was no statistically significant difference in major bleeding rates at 3 months between the treatments (OR 0.45, 95% CI: 0.18, 1.11). No significant heterogeneity was detected (P=0.77). The meta-analysis had 38% power.
Mortality (7 RCTs): there was no statistically significant difference in mortality at 3 months between the treatments (OR 1.19, 95% CI: 0.78, 1.83). No significant heterogeneity was detected (P=0.89). There was no statistically significant difference in mortality due to PE between the treatments (OR 1.64, 95% CI: 0.39, 6.91). The meta-analysis had 66% power of detecting a 50% reduction. There was no statistically significant difference between treatments in mortality due to cancer mortality (6 studies; OR 1.12, 95% CI: 0.63, 1.98). No significant heterogeneity was detected (P=0.95).
There was no statistically significant difference between treatments in mortality for patients who were known to have cancer at baseline (126 patients; OR 1.13, 95% CI: 0.54, 2.38).
There was a non-statistically significant linear trend between LMWH dose and VTE recurrence (r2=0.194, P=0.33) and a significant linear trend between dose and bleeding complications (r2=0.65, P=0.027).
The results for VTE recurrence and major bleeding were similar after excluding one study published only as an abstract.
After excluding the one study that used a different initial treatment in the two groups, the pooled OR for VTE recurrence was 0.90 (95% CI: 0.51, 1.6). No significant heterogeneity was detected (P=0.26).