Regarding the rate of VTE recurrences, another of my published systematic reviews of anticoagulants for VTE searched for clinical evidence of “rebound hypercoagulation” after discontinuing oral anticoagulants (i.e., a spike in the rate of VTE recurrences in the weeks and months immediately following the stoppage of anticoagulants).(29) In this review (20 trials, n = 5822, average age = 60.5 years), the VTE recurrence rate while taking warfarin or other oral anticoagulant was 0.38%/month (compared with < 0.02%/ month for a 60-year-old with no previous VTE(35)). During the first two months off oral anticoagulants, the rate spiked to 1.57%/patient-month (confirming clinical evidence of rebound hypercoagulation). For the remainder of the time on study (mean = six months), the rate of VTE recurrences after discontinuing oral anticoagulants was 0.56%/patient/month. During the total of eight months off of anticoagulants, about 6% of patients developed recurrent VTE. Findings from long-term follow up studies show that this initial high initial rate of VTE recurrence (1.57%/month in my meta-analysis) subsequently slows down to about 0.2%/month, which is at least 10 times the incidence in people of the same age without previous VTEs (≤ 0.02% / month(35)).
In population-based VTE recurrence studies, VTE patients had the following rates of VTE recurrences in the first three years: 20%,(36) 15%,(37) and 9.1%.(38) So, on average, the VTE three-year recurrence rate is about 15%. In the two longest term population based studies published that followed people after an episode of VTE, the cumulative number of VTE recurrences were 30% at 10 years(39) and 30.3% at eight years.(36) Given that Ms. Clinton is now more than three years past her CVT episode and more than 17 years past her VTE episode, her chance of VTE recurrence over the next 10 years, based on all this data, is in the range of 20% (i.e., about 2% per year).
Factored into this estimate are that her DVT was not provoked by surgery, trauma, or prolonged bed rest. Unprovoked DVT is associated with higher VTE recurrence risk. Also, airplane flights > six hours long have been found to increase risk of VTE. A systematic review of 25 studies of VTE risks with airplane flights concluded that people with one or more risk factors for VTE (e.g., age ≥ 65 years-old) who are taking a flight > six hours in duration should consider wearing compression stockings or taking prophylactic low-molecular-weight heparin.(40) Choosing to follow this guideline could result in very frequent and very unnecessary injections of low-molecular-weight heparin in a frequent-flying President.