Incidence of superficial venous thrombosis in primary care and risk of subsequent venous thromboembolic sequelae: a retrospective cohort study performed with routine healthcare data from the Netherlands.

OBJECTIVES

Recent studies in referred populations of patients with superficial venous thrombosis (SVT) report risks of venous thromboembolic (VTE) sequelae (deep vein thrombosis or pulmonary embolism) as high as 25%. Likely, these estimates are lower in non-referred patients, but large-scale population-based studies are lacking. We aimed to estimate the incidence rate of SVT in primary care and quantify its risk of VTE sequelae.

DESIGN

A retrospective cohort study, using International Classification of Primary Care coding (K94.02) combined with free text searching (synonyms for SVT) to capture all SVT events. All patients were followed up for 3 months using manual free text searching.

SETTING

Primary care.

PARTICIPANTS

All patients enlisted with general practitioners within the Utrecht General Practitioner Network between 2010 and 2016 (1 534 845 person-years follow-up).

MAIN OUTCOME MEASURES

The incidence rate of SVT was expressed as the number of SVT events per 1000 person-years of follow-up and the 3-month cumulative incidence of VTE events was calculated. Logistic regression analysis was used to compare patients with SVT with and without VTE sequelae.

RESULTS

A total of 2008 SVT cases were identified, that is, an SVT incidence rate of 1.31 (95% CI 1.25 to 1.37) per 1000 person-years follow-up, with higher rates notably with increasing age. VTE sequelae occurred in 83 patients; 51 at the time of SVT diagnosis and 32 patients during follow-up (total cumulative incidence of 4.1%; 95% CI 3.3% to 5.1%), and were more frequent in those with an active malignancy (OR 2.19; 95% 0.97 to 4.95) and less frequent in those with varicose veins at baseline (OR 0.57, 95% CI 0.34 to 0.94).

CONCLUSION

We found an incidence rate of SVT in primary care of 1.31 per 1000 person-years. The risks of VTE sequelae was relatively low at 4.1%, with the highest risk in patients with cancer and in those who experience an SVT in the absence of varicose veins.