Clinicians should resist the temptation to label patients with suspected recurrent VTE while on anticoagulant therapy as a true therapeutic failure.
Professor Marc Rodger, head of haematology at the Ottawa Blood Disease Center, told the ISTH Congress that while suspected VTE on therapy was common, confirmed recurrent VTE was not.
As a consequence, how to manage the clinical dilemma was largely an evidence-free zone.
“Confirmed recurrence on therapy is a pretty rare bird – 1-2% in the first year and it probably diminishes thereafter. So it becomes a challenge to do randomised trials in a prospective cohort when you’re dealing with a fairly rare occurrence,” he told the limbic.
Professor Rodger told the Congress that many patients would have residual disease, which confounded the diagnosis of a recurrent event.
Distinguishing between old and new events on the basis of comparative imaging was important but he warned many proposed imaging characteristics or tests had not been validated.
Similarly, there was limited data on the value of D-dimer tests, with or without clinical pre-test probability assessment, to differentiate acute versus chronic disease.
Professor Rodgers said patients with residual disease only should be continued on their current treatment.
He said non-compliance with therapy was a common cause of confirmed recurrence.
While asking the patient was a good start, he also recommended requesting some objective evidence such as INR for patients on warfarin or an anti-Xa for DOAC users.
Where memory issues may be leading to compliance issues, he suggested strategies including the use of pill boxes and smart phone reminders as well as enlisting the support of family, friends and carers.
Affordability of medication was another potential problem impacting compliance. Nevertheless most patients should be re-started on the approved first-line anticoagulants.
Professor Rodger said patients with cancer, anti-phospholipid antibody (APLA) syndrome, heparin-induced thrombocytopenia (HIT), paroxysmal nocturnal haemoglobinuria (PNH) and myeloproliferative disease (MPN) were all high-risk groups for a recurrent VTE.
Changing or escalating their therapy – for example, treating APLA with warfarin or switching to low molecular weight heparin – may be warranted.
However there was a general lack of randomised controlled trials or prospective trials to guide those decisions.
“Retrospective cohorts will not be high quality evidence but will hopefully guide us,” he said.