Single center evaluation on the use of conditionally ordered low molecular weight heparins in malignant hematology patients with venous thromboembolism.

Background: Cancer and cancer-related treatments are significant independent risk factors for malignant hematology (MH) patients in developing venous thromboembolism (VTE). Treatment of VTE in MH patients at the Princess Margaret Cancer Centre is predominantly initiated with low molecular weight heparin (LMWH) in accordance with guidelines. While guidelines recommend against LMWH use in patients with thrombocytopenia, prescribers may order LMWH conditionally based on platelet values. Currently, there is a lack of consistent practice with variation in both the use of conditional orders as well as the threshold of platelet values for conditional orders. The objectives of the study were to (a) describe the use of conditionally ordered LMWH based on platelet values; (b) determine its safety by measuring administration concordance with conditional orders and bleeding event rates during inpatient admission; and (c) determine its efficacy by measuring the rate of worsening VTE or recurrence during inpatient admission.

Methods: Electronic records of MH inpatients admitted between January 2017 and December 2019 and who were administered at least one dose of an LMWH for the treatment of VTE were screened.

Results: One hundred and eight patients were screened to obtain 50 eligible patients with a median age of 59 years (SD = ±18.8 years). The most frequent MH diagnosis was acute lymphoblastic leukemia (30%). Sixty percent (n = 30) of patients received conditional orders. Out of 571 administrations, 543 (95%) were administered concordantly (Χ²(1) = 472, p < 0.0001). In this group of patients, 8 patients had either documented bleeding or experienced a drop in hemoglobin >10 g/L within a 72 h time frame. No patients experienced a recurrent VTE during inpatient treatment (for up to 40 days post-admission).

Conclusions: It appears that conditionally ordered LMWH can be concordantly administered and is safe and effective in the treatment of VTE in MH patients experiencing thrombocytopenia. There were no reports of worsening or new VTE in our small sample.