DVT plane risk may be lower than thought
Bupa investigative news - 11 July 2003 (updated 14 August 2003)
written by Rachel Newcombe, reporter for Bupa's Health Information Team
In recent years, deep vein thrombosis (DVT) has been dubbed "economy class syndrome", after being linked with cases in aeroplane passengers. But, new research suggests the risk might not be as bad as previously thought and that business class flyers are at the same risk as economy passengers.
What were the headlines?
The study results were reported in a journal in South Africa, and the findings quickly made it into the UK media, many via correspondents based in Johannesburg, hot on the heels of news that court cases against airline companies because of DVT had failed.
The reports looked at the research and what it could mean for air companies, and the reports gained headlines such as, "Risk of DVT may be overstated, say scientists", "Air passenger study challenges DVT theories", and "Risk of clots in air travel over-hyped".
What is the bigger picture?
The study was called BEST - Business class versus Economy class Syndrome as a cause of Thrombosis - and was led by Professor Barry Jacobson, head of clinical haematology at the National Health Laboratory Service and head of the surgical research unit at the University of Witwatersrand in Johannesburg. It was published in the South African Medical Journal.
Passengers travelling from Johannesburg to London were recruited to the study. In total 899 people took part - 180 flying in business class and 719 in economy. Clinical tests and blood samples were taken before and after the flight. They looked for D-dimers - proteins that are released into the circulation when a blood clot is formed or broken down in the body - and Factor V Leiden - a genetic mutation that puts carriers at a five times greater risk of developing blood clots.
The researchers discovered the risk of developing DVT after a long-haul flight seemed to be low - at about 1 per cent of all long-haul passengers.
"The results of the research showed, encouragingly, that the incidence of deep vein thrombosis was much lower than previously reported in other research or in anecdotal evidence. We found that none of our passengers studied developed an ultrasound-proven or a clinically significant DVT," explained Professor Jacobson.
However, up to 10 per cent of long-haul flyers had abnormally elevated levels of D-dimers in their blood, suggesting that they had potentially developed small unrecognisable clots. Interestingly, these raised D-dimer levels were not found only in economy-class passengers, business-class passengers were affected just as often - suggesting legroom and space might not be such an issue.
According to Professor Jacobson, the usual advice to help to reduce the risk of DVT, such as exercising the feet, stretching one's toes while sitting and drinking plenty of water, had no effect on the levels of D-dimers. In fact, he claims that taking aspirin - one possible risk-reduction method - may actually raise D-dimers. One of the few factors that did correlate with a raised risk of DVT was the presence of the Factor V Leiden gene.
"What this means," said Professor Jacobson, "is that the airlines and the medical profession will now obviously have to rethink the way they address this issue to prevent injury and deaths."
"Even though the percentage of people developing this condition is very small, perhaps as low as 1 per cent or less of all long-haul passengers, the sheer volume of air passenger numbers is sufficient to present a significant problem to the airlines, the medical profession, the medical insurance industry, as well as individuals who may believe that they are at risk of developing DVT," he said.
"Although there is considerable scientific debate as to how great the risk of DVT is from longhaul air travel, prolonged immobility - as occurs during long journeys by air, coach or car - is known to be associated with an increased risk of DVT. When someone is sitting down for a long time their blood tends to pool in their lower leg veins causing swelling and increasing the chance that the blood will clot and form a DVT."
Dr Annabel Bentley,
assistant medical director
Bupa Group
What does this mean?
Dr. Jane N. Zuckerman, director of the academic centre for travel medicine and vaccines and the Royal Free travel health centre, wasn't surprised that economy and business class passengers fared the same. "There's not really a great difference between the legroom in economy and business class, depending on which airline you fly with. In some aircrafts they now have beds in first class and some business class areas have reclining seats. However, all that does is assist in people's immobility, it doesn't actually increase movement."
She added that, "The important aspect is to be able to flex the calf muscles, move about and keep hydrated. The amount of legroom, in my view, is a red herring."
Farrol Kahn, director of the Aviation Health Institute (AHI), "We would agree with the researchers that it's not simply a case of economy class syndrome as it affects people throughout the whole aircraft." However, his view goes one step further, suggesting the environment may play a part. "It's the actual aircraft environment that triggers the DVT," he said. "We've had deaths reported in flying beds, for example, which shows that it's not simply the prolonged sitting or prolonged immobility, but rather the dry air, less oxygen (up to 25 per cent less) and lower pressure which contribute to DVT."
However, although interested in the research, Mr. Kahn believes "there are several flaws" in the study. "For a start, it isn't the largest study ever carried out [as some reports have suggested] - Professor Belcaro has studied nearly 3,000 travellers as part of the LonFlit research," he said. "Also, the D-dimer test is not a diagnosis of DVT and we'd disagree that water, flight socks and taking aspirin aren't useful as other research has shown otherwise."
The idea that some people are at a greater risk of DVT and that genetic aspects may play a part didn't come as a surprise to Dr. Zuckerman. "It's well recognised that some people are more genetically susceptible to thrombotic [blood clotting] disorders, such as DVT, because they have haematological markers in their blood which result in thrombi [blood clots]," she explained. However, she doesn't believe airport screening would be cost effective, as it only affects a small number of people.
According to the Department of Health (DoH), there's some evidence that long-haul flights, particularly when people have little or no exercise, may increase the risk of DVT. However, they say the risk is "small" and add that it's hard to know if it's the flight itself that actually causes DVT or the fact that more susceptible people are travelling.
ACTION POINTS
To help reduce the risk of DVT while flying long haul:
- avoid crossing your legs while seated
- walk around whenever possible
- carry out foot and leg exercises while seated
- keep hydrated by drinking enough water
- avoid alcohol and caffeinated drinks
- stand up and stretch your arms and legs from time to time
- wear loose fitting clothes
What does this mean to me?
The Department of Health (DoH) says that one in 2,000 people get DVT every year. The risk of DVT is increased by:
- being more than 40 years of age
- With a personal or family history of blood clots
- cancer treatments
- heart failure or circulation problems
- an inherited clotting disorder
- recent knee or hip surgery
- recent pelvic surgery (for example hysterectomy)
Women who are pregnant or recently had a baby, and those taking HRT or the oral contraceptive also have an increased risk.
But for those worried about DVT and flying, there are ways to reduce the risk and, contrary to some of the views of Professor Jacobson, other experts do believe they're worthwhile. "We would recommend that people should definitely wear flight socks," said Farrol Kahn. "Several studies have shown these to be of benefit and it reduces the risk by up to 90 per cent."
Dr. Zuckerman agreed, saying, "There's certainly reports that flight socks contribute to the prevention of DVT. In a clinical hospital setting we've been using similar socks with vascular patients for years."
DVT isn't just something to be aware of when flying - it's equally valid during any activity when that requires you to be immobile for long periods. Other studies have found risks when driving for long periods and even when sitting in front of a computer for hours on end.
Summary
DVT isn't something to be alarmed about and maybe less common than first thought, but by being aware and taking simple precautions when flying - whether in first, business or economy class - the risk can be reduced.
Further information
- Bupa DVT factsheet
- Bupa DVT article
- Aviation Health Institute
- Department of Health DVT information
- Qantas in-flight exercise guide
- South African Medical Journal abstract - The BEST study — a prospective study to compare business class versus economy class air travel as a cause of thrombosis
