Frequency of “Special Population” Characteristics among Venous Thromboembolism Patients in Clinical Practice: Implications for Anticoagulant Therapy.

Abstract

Background: Consensus guidelines recommend the use of low molecular weight heparin (LMWH), dosed by patient weight, over unfractionated heparin (UFH) as first-line therapy for the initial treatment of venous thromboembolism (VTE) and as monotherapy for the long-term treatment of cancer-related VTE. However, caution is advised for certain “special populations”: in patients with renal impairment or in the elderly, weight-based dosing may be excessive, while capping the dose in obese patients as recommended by some LMWH manufacturers may lead to inadequate dosing.Objectives: We evaluated the frequency of characteristics such as renal impairment, advanced age, obesity and cancer among patients diagnosed with VTE in clinical practice, and assessed the impact of these characteristics on type and dose of medication prescribed to treat VTE.Methods: Medical records, thrombosis clinic charts and vascular lab reports from April 1, 2004 to March 31, 2005 were systematically searched to identify consecutive patients with objectively diagnosed VTE at 2 large university-affiliated hospitals in Canada. Trained research assistants abstracted patient records using study-specific case report forms. Data on age, sex, serum creatinine at time of VTE diagnosis, weight, presence of active cancer, type of VTE event, treatment initiated and dose of LMWH were recorded. Creatinine clearance (CrCl) was calculated using the Cockcroft Gault formula. Proportions of patients with renal impairment, advanced age, obesity and cancer were calculated. Type of treatment and appropriateness of LMWH dosing in various patient subgroups were determined.Results: 524 patients (Montreal 293; London 231) with VTE were identified, of whom 19% had PE and 81% had DVT. The average age was 62 years, with 31% of patients >75 years and 18% patients > 80 years. Overall, treatment initiated was LMWH and warfarin (71%), LMWH monotherapy (13%), UFH and warfarin (4%), IVC filter alone (4%) and other (8%). Moderate renal impairment (CrCl 30–50 ml/min) was present in 11% of patients and severe renal impairment (CrCl <30 ml/min) in 5%; only 58% of patients had normal renal function (CrCl >80 ml/min). Although mean CrCl was lower in patients who received UFH vs. LMWH (64 vs. 96 ml/min, p=0.003), an anticoagulant regimen that included LMWH was administered to 67% of patients with severe renal impairment and 83% of patients with moderate renal impairment. Body weight was >100 kg in 15% of patients. Underdosing of LMWH by 10% or more was documented in 36% of patients >100 kg compared with 8% of patients < 100 kg (p<0.001). Active cancer was present in 26% of patients. Patients with active cancer were more likely to be treated with LMWH monotherapy that those without cancer (32% vs. 7%, p<0.001).Conclusions: In clinical practice, renal impairment, advanced age, obesity and cancer are frequently present in patients with VTE. A significant proportion of patients with these features did not receive recommended type or dose of medication to treat VTE. Further research should address ways to improve implementation of VTE treatment guidelines into day-to-day clinical practice.