An epidemiologic evaluation of hospitalizations of elderly Medicare beneficiaries due to adverse reactions to anticoagulant therapy using claims data

Abstract

The objective was to examine a representative population of elderly persons in the United States to (1) provide an estimate of the number of persons taking oral anticoagulants, (2) estimate the rate of anticoagulant adverse drug reaction (ADR) hospitalizations, (3) describe patient demographic and clinical characteristics, and (4) examine patient and provider characteristics in relation to an anticoagulant ADR. The retrospective case-control study used the Health Care Financing Administration's Medicare program claims and administrative data. The case-control subjects were "presumed" to be being monitored for anticoagulant treatment. The selection criteria excluded those with less than three prothrombin time tests PTs and no claim indicating one of the following diagnoses; pulmonary embolism, atrial fibrillation with embolism or, deep vein thrombosis. The number of subjects in the study was 1,135 cases and 7,133 controls. The estimated number of persons "presumed" to be monitored for anticoagulant therapy was 2 million. Incidence rates of ADR hospitalizations and anticoagulant ADR hospitalization per 1,000 hospitalizations were found to be 22.99 and 1.17. This study found that although anticoagulant ADRs are rare, the finding may be an underestimate. The only patient demographic characteristics found to be associated with ADRs was gender. Females were at risk for an ADR. The relationship between structure, process, and outcomes, (an effectiveness model) identified factors that increase the risk for an anticoagulant ADR hospitalization. Persons who had PTs done in physician office laboratories were at slightly greater risk for an adverse outcome than persons who had PTs done in commercial laboratories. Persons in the case-control group had a high mean number of interactions with the health care system, between 1 and 2 a week suggesting that persons on anticoagulant therapy account for a relatively high amount of utilization. Carcinoma, hypertension, renal insufficiency, congestive heart failure and hepatic disorders were confirmed as risk factors for an adverse outcome. But, because of the under-reporting of ADRs, it is likely that there is misclassification of cases as controls. Thus, there is bias towards the null for all the risk factors, and if anything, those factors associated with ADRs are underestimates.