Five in every jumbo at risk from blood clots

By MARTIN JOHNSTON health reporter

More than one in every 100 air travellers on long-haul flights develops blood clots, a study has found.

New Zealand researchers tested blood samples from 1000 people after flights of four hours or more and found that 14, or 1.4 per cent, had formed clots.

This would mean that on a jumbo jet carrying 400 people, an average of more than five passengers could be at risk after a long-haul flight.

The researchers say that many of those tested in the study lacked any obvious, identifiable risk factors for clots when they were assessed and gave a blood sample before their flights.

The study is one of the world's most comprehensive into links between clots, which are potentially fatal, and air travel.

Prolonged immobility puts people at greater risk of clots forming in leg veins. In some cases the clots shift to the lungs, where they can cause chest pain, breathing problems and, in the worst cases, death. Many travellers came to fear so-called deep-vein thrombosis (DVT) after the death in 2000 of Emma Christoffersen, 28, from a clot believed to have formed during a flight from Australia to England.

A British study put the risk of forming clots at one-in-10 among long-haul fliers, but the travellers in that research were all over 50 and older people are at greater risk of developing clots. Other risk factors can include family history of clots, or being obese, pregnant or a smoker.

The 1000 travellers in the New Zealand study, which was of 18-70-year-olds and included some All Blacks, were considered to be at low to moderate risk of forming a clot.

Because so few developed clots, the research team was unable to evaluate the role of known risk factors and it now plans to extend the study.

"We want to work out how important the different risk factors are for travellers' thrombosis," one of the researchers, Professor Richard Beasley of the Medical Research Institute of New Zealand, said yesterday.

Researchers from the Wellington-based institute, Green Lane Hospital in Auckland and Christchurch Hospital want to recruit 250 volunteers who have been diagnosed with flight-related DVT in the past three years.

The findings of the original study were disclosed to an Auckland ethics committee but the full details are being kept under wraps until they are published in a medical journal, probably next year.

In the preliminary results, announced in November, clots had formed in eight people. In three of them, the clots had shifted to their lungs and were potentially serious but not life-threatening.

Some of those who formed clots had been taking aspirin, leading Dr Rodney Hughes, who headed the original study, to say that the drug was at best of dubious benefit in preventing travellers' thrombosis.

The study also aimed to discover if fluid intake, flight duration and seat position altered the risks of long-haul passengers forming clots.

Feature: Economy class syndrome

nzherald.co.nz/health