Blood-thinning medications associated with increased risk of complications from having blood in urine

Antithrombotic (reduces the formation of blood clots) medications, such as warfarin and aspirin, are among the most commonly prescribed and also among the medications most commonly associated with adverse events. While hematuria represents a less life-threatening adverse event than intracranial or gastrointestinal bleeding, it is common and involves diagnostic evaluation including abdominal imaging and invasive testing and management. The prevalence, severity, and risk factors for hematuria associated with the use of anti-thrombotic agents are largely unknown.

Robert K. Nam, M.D., M.Sc., of Sunnybrook Health Sciences Centre, University of Toronto, and colleagues conducted a study that included citizens of Ontario, Canada, ages 66 years and older, and examined rates of hematuria-related complications among patients taking antithrombotic medications.

Among 2,518,064 patients, 808,897 (average age, 72 years) received at least one prescription for an antithrombotic agent over the study period (2002-2014). Over a median follow-up of 7.3 years, the rates of hematuria-related complications (defined as emergency department visit, hospitalization, or a urologic procedure to investigate or manage gross hematuria [blood in the urine that can be seen with the naked eye]) were 124 events per 1,000 person-years among patients actively exposed to antithrombotic agents vs 80 events among patients not exposed to these drugs.

While there was variation between medications, this association was present for all medications examined. Readily identifiable factors, including patient age, male sex, comorbidity, and preexistent urologic disease, were significantly associated with rates of gross hematuria.

The study notes some limitations, including that owing to funding eligibility for prescription medications in Ontario, the cohort was restricted to patients ages 66 years and older. Given the interaction between age and the association of antithrombotic therapies with hematuria-related complications, these results are not directly applicable to younger patients.