AntiphosphoLipid Testing in Patients with Unprovoked VEnous ThRomboembolism

Background

Patients with VTE who have ‘triple positive’ APLS are known to have a high risk of recurrent VTE.

VKAs are more effective at ameliorating this risk than DOACs particularly in those with triple positive disease or arterial thrombosis. However, management of patients with single/double positive disease with VTE alone is unclear with either VKA or DOACs suggested.

A2PLS (yet to be published – data presented ASH 2022) suggested that LAC positivity may predict a similar VTE recurrence rate to triple positive disease.

Recommendations and Current Situation

Current BSH, NICE and ASH guidelines are conflicting as to which patients with VTE should be tested for APLS. A recent clinician survey (to be presented at BSH) has shown a preference in the UK for identifying APLS to advise whether switching from DOAC to VKA is required.

Behind this varied guidance is the fact that there is little evidence to suggest which patients should be tested for APLS despite a prevalence in 10-15% with unprovoked VTE

In a large multicentre audit (to be presented at BSH), we found highly variable practice in thrombosis clinics regarding who was tested for APLS. We found that age < 65 years was a discriminator for APLS positivity. There were also low overall rates of triple positive APLS detection.

Proposal

We propose an observational study (suggested cluster randomised study) of universal testing vs selective testing for APLS with follow up for 1-2 years dependent on APL results

  • Patients: all patients to a thrombosis clinic with a new unprovoked VTE

  • Intervention: selective testing for APLS (selected based on TBC criteria)

  • Comparison: testing of all patients.

  • Outcomes:

  1. Primary outcome: Rate of positive APL testing

  2. Secondary outcomes: Recurrent thrombosis rates (patients with single/double positive APL will be followed for 2-years for prospective, observation data collection), change to VKA based on testing results, difference in APL testing rates, presence of clinical features for APLS