The obesity paradox exists in the context of VTE with patients with a BMI ≥30 more likely to have a VTE but less likely to die than patients with VTE and a normal BMI.

According to results presented at the ISTH 2020 Virtual Congress, it’s the underweight patients with VTE who are most at risk of all-cause mortality and of major bleeding.

Data from the global GARFIELD-VTE registry of more than 10,000 patients with VTE found the all cause mortality rate was 7.31 per 100 person years in normal weight patients, 4.81 in overweight patients, and 3.56 in obese patients (HR 0.66).

Co-investigator Associate Professor Harry Gibbs told the limbic the underweight patients should probably be the focus.

“Those who are underweight do very poorly. They have a mortality rate of 25 per 100 person-years over two years. It’s basically 25% over two years which is extremely high mortality.”

“And that’s because there is something wrong with them. They have got cancer, end stage heart failure, COPD or something else and the VTE is a marker for the fact that they are getting very sick.”

In contrast, the overweight and obese patients probably have relatively minor risk factors for VTE  like being on the oral contraceptive pill or long distance travel.

“And so you remove that risk factor and they don’t often have much else going on with them apart from the fact they are overweight. So they tend to do better after that.”

He said the normal weight patients were probably a more heterogeneous group including some of whom will have cancer, major trauma, or an unprovoked VTE.

Associate Professor Gibbs, program director for outpatients and deputy director of general medicine at Alfred Health, said as well as the very high mortality, underweight patients with VTE have a 3-4 times higher risk of major bleeding than the normal, overweight and obese patients (event rates 6.29, 1.95, 1.63 and 1.63 per 100 person years respectively).

“So it tells you a few things – that they are at risk and likely to have significant intercurrent illness but the other thing about them is that the treatment is a bit more difficult. When you have got someone who is normal weight or up to about 120kg, we are pretty confident about how to treat them.”

“When you have someone who is really skinny and cachectic really, it becomes a bit more difficult with how to dose them. Should you reduce the dose and to what extent? If you don’t give them enough they will have a recurrence; if you give them too much they will bleed.”

The real world study found obese patients were more likely to remain on anticoagulant therapy over two years than normal weight patients (48.5% v 37.6%) yet it was probably not necessary.

“To me the message is that they [obese patients] are a group who don’t actually present with higher mortality, major bleeding or risk of recurrence compared to those who are normal weight.

“Obesity is not a reason to continue with anticoagulation indefinitely,” he said.