P0810DOSAGE REDUCTION OF LOW MOLECULAR WEIGHT HEPARIN IN PATIENTS WITH RENAL DYSFUNCTION: EFFECTS ON ANTI-XA LEVELS AND CLINICAL OUTCOMES

Background and Aims To prevent bio-accumulation of low molecular weight heparins (LMWHs) in patients with an impaired kidney function, guidelines recommend dosage reduction and anti-Xa monitoring. The aim of this study was to investigate the effect of pre-emptive dosage reduction of LMWH on anti-Xa levels. Furthermore, we investigated the association between anti-Xa levels and bleeding, thrombotic events and mortality. Method In this single center study, we followed 499 patients with an estimated glomerular filtration rate (eGFR) below 60 ml/min/1.73m2 in whom anti-Xa levels were measured. We observed how many patients had anti-Xa levels that fell within the target range (between 1.0 U/ml and 2.0 U/ml with once daily LMWH and between 0.6 U/ml and 1.0 U/ml with twice daily LMWH), with a standard protocol of a pre-emptive dosage reduction of LMWH (25% reduction in patients with an eGFR between 30 and 60 ml/min/1.73m2 and a reduction of 50% in in patients with an eGFR below the 30 ml/min/1.73m2). Furthermore, Cox proportional hazard analyses were used to estimate hazard ratios with 95% confidence intervals (CIs) to investigate the association between anti-Xa levels and major bleeding, thrombotic events (ischemic stroke or venous thrombosis) and mortality within three months of follow-up. Hazard ratios were adjusted for age, sex, body mass index, type of LMWH, once or twice daily dosing, antiplatelet drug use, indication for anticoagulation, comorbidities, hemoglobin concentration and eGFR. Results In a cohort of 499 patients (445 dalteparin and 54 nadroparin users), the median anti-Xa level was 0.44 U/ml (IQR 0.21-0.75) for the total group (n=499). A pre-emptive dosage reduction of LMWH led to adequate levels of anti-Xa in only 19% of the patients (12% for the dalteparin users and 50% for nadroparin users). Of the 499 patients, 104 patients had a major bleeding, 27 had a thrombotic event and 146 died within three months. We did not find an association between anti-Xa levels and bleeding or mortality (Table 1). An anti-Xa level below the target range was associated with a non-significant increased risk estimate for thrombosis (HR 2.5, 95% CI 0.7-8.8) after adjustment (Table 1). Conclusion Pre-emptive dosage reduction of LMWH leads to low anti-Xa levels in a large proportion of patients and may lead to an undertreatment of patients with an impaired kidney function.