Primary care diagnosed multimorbidity and risk of venous thromboembolism in Sweden

Background: Multimorbidity, the co-occurrence of two or more non-communicable diseases (NCDs), is common and has been linked to venous thromboembolism (VTE). Whether multimorbidity diagnosed in primary-care is associated with incident VTE remains unclear. We aimed to examine this association. Methods: Multimorbidity was defined using Swedish primary-care data. Individuals without prior VTE were included, and incident VTE was identified through the Swedish National Patient Register. Primary-care multimorbidity was defined as two or more NCDs. Subdistribution hazard ratios (subHRs) for VTE were estimated adjusting for sociodemographic factors and acquired and inherited VTE risk factors. The VTE risk of nine disease clusters were investigated. Results: Among 8,170,329 included individuals, 2,183,236 (26.72%) had primary care-diagnosed multimorbidity. Adjusted subHR for VTE among individuals with multimorbidity was 1.36 (95%CI 1.34-1.39). A dose-response association was observed, a subHR of 1.62 (95%CI 1.57-1.67) for individuals with ≥5 NCDs. There were significant interactions between multimorbidity and sex and country of birth. Seven of nine multimorbidity clusters were associated with increased VTE risk. Conclusion: Primary care-diagnosed multimorbidity is an independent, dose-dependent risk factor for VTE. The association between several disease-clusters and VTE suggests potential value in cluster-based risk prediction.