Class of air travel and risk of DVT

The only study that I can find that measures the effect of class of
travel on the chance of getting a DVT is this on (all the other
articles seem to refer back to it):
S Afr Med J. 2003 Jul;93(7):522-8.
The BEST study--a prospective study to compare business class versus
economy class air travel as a cause of thrombosis.
"
Only 434 subjects had a full venous duplex scan performed. None had
ultrasonic evidence of venous thrombosis. Nine passengers tested at
departure had elevated D-dimer levels and these volunteers were
excluded from further study. Seventy-four of the 899 passengers had
raised D-dimers on arrival. Twenty-two of 180 business class
passengers (12%) developed elevated D-dimers compared with 52 of 719
economy class passengers (7%). There was no significant association
between elevation of D-dimers and the class flown (odds ratio (OR)
0.61, p = 0.109).
"
I'd imagine that a huge amount of money, potentially, rests on this
evidence, so I'm surprised that this is the only study. I haven't got
Dr Jacobson's e-mail address at Wits, nor the whole text of the study
yet, but I'll follow these up to understand more detail and if there
was any special funding.
I find something curious about the above, though, maybe somebody with
some knowledge of statistics can help explain it.
1. If all air passengers were the same, and there was no bias caused
by the class of travel, then you'd expect, I'd have thought, to find
the same raised D-dimers (the proxy for potential DVT in the study)
in
both populations. To me, finding 14% in on population and 7% in the
other would suggest that the first population was twice as likely to
suffer the effect.
2. Clearly the size of study is important. So, though the whole study
includes nearly 900 passengers, the study only examines 180 business
class passengers. So, these are less likely to be representative than
those not in business class.
3. Isn't it also likely that those flying in Business class will have
other characteristics that differ that might be significant in their
risk of DVT? Shouldn't these factors be exluded before a comparison
is
made?
4. How, then, do they come to the conclusion that there is no effect?
A simple minded reading of the conclusion suggests to me that
Business
Class might be more dangerous. However, if Business Class passengers
are older, fatter and maler than economy class passengers, all of
these being predisposing factors (some might even have been in
Business Class specifically because they were higher risk passengers
for other reasons) might, when excluded, show that Business Class is,
in fact, much safer.
How can this 2003 study be the only thing on which we can base our
conclusions?
Is it possible that airlines have tested this themselves (I'd find it
odd if this had not occurred to any airline) and decided not to
publish the results?
After all, if business class was much safer, then there would be
considerable pressure to increase the space in economy, rather than
put these passengers at a health risk - the conclusion of the study
removes this pressure. Alternatively, if it is actually the case that
business class is more dangerous, then fewer people would pay three
times the price for it - at least on health grounds.

Peter Brooks wrote:
The only study that I can find that measures the effect of class of
travel on the chance of getting a DVT is this on (all the other
articles seem to refer back to it):

Hmmm.. perhaps all those pre-flight drinks in business and first class
have a bit of blood thinning affect

Just in case, I try to take an aspirin before flying anymore. Sardine
class being what it is, y'know?

In article ,
Goomba wrote:

Peter Brooks wrote:
The only study that I can find that measures the effect of class of
travel on the chance of getting a DVT is this on (all the other
articles seem to refer back to it):

Results of the BEST study show no class-related effect. In fact, on
one possible risk factor (D-dimer) business class was more likely to
show raised levels

Hmmm.. perhaps all those pre-flight drinks in business and first class
have a bit of blood thinning affect
You would think it would cause dehydration.


Just in case, I try to take an aspirin before flying anymore. Sardine
class being what it is, y'know?

Get up every couple hours and walk around. Drink fluids (and not
alcoholic beverages). Flex your legs often. Aspirin has been found
useful and not useful depending on the study. Probably put it in the
"can't hurt" category either way . Those with either a family or
personal history of clotting problems should probably see their docs to
see if low-molecular weight heparin and/or support stockings might be a
good idea.
In addition to certain genetic traits, risk factors identified by a
2007 World Health Organization Report on the hazards of global travel
include:
o Age of over 40 years
o History of blood clots either personally or in the family
o Living with or being treated for cancer
o Obesity
o Extremes of height
o Recent surgery, especially on knees and hips
o Pregnancy or hormone therapy such as birth control pills or hormone
replacement therapy for menopause

Just got done doing an article on the subject, so thanks to the
boys and girls at the NIH Clinical Center in Bethesda and Aerospace
Medical Association in Alexandria. (g).

On May 26, 5:08*pm, Kurt Ullman wrote:
In article ,

*Goomba wrote:
Peter Brooks wrote:
The only study that I can find that measures the effect of class of
travel on the chance of getting a DVT is this on (all the other
articles seem to refer back to it):

* * Results of the BEST study show no class-related effect. In fact, on
one possible risk factor (D-dimer) business class was more likely to
show raised levels

Hmmm.. perhaps all those pre-flight drinks in business and first class
have a bit of blood thinning affect

* * *You would think it would cause dehydration.



Just in case, I try to take an aspirin before flying anymore. Sardine
class being what it is, y'know?

* Get up every couple hours and walk around. Drink fluids (and not
alcoholic beverages). Flex your legs often. Aspirin has been found
useful and not useful depending on the study. Probably put it in the
"can't hurt" category either way . Those with either a family or
personal history of clotting problems should probably see their docs to
see if low-molecular weight heparin and/or support stockings might be a
good idea.
* * *In addition to certain genetic traits, risk factors identified by a
2007 World Health Organization Report on the hazards of global travel
include:
o *Age of over 40 years
o *History of blood clots either personally or in the family
o *Living with or being treated for cancer
o *Obesity
o *Extremes of height
o *Recent surgery, especially on knees and hips
o *Pregnancy or hormone therapy such as birth control pills or hormone
replacement therapy for menopause

* * * * Just got done doing an article on the subject, so thanks to the
boys and girls at the NIH Clinical Center in Bethesda and Aerospace
Medical Association in Alexandria. (g).

Asprin is not useful. It does reduce the risk of arterial thrombosis,
but the flight risk is of venous thrombosis. Asprin can cause gastric
problems, though, which is not good for you.

If you are in a high risk group for a DVT (see the scale at:
http://www.fleetstreetclinic.com/ip1...nu=4&sub_id=52 )
then you should take low molecular weight heparin before a very long
flight (12 hours), take an aisle seat, drink plenty of liquids, but
no alcohol and not take sleeping tablets (though the study I reported
didn't find an effect for alcohol or sleeping tablets). It might also
be a good idea to fly business class - though, strangely, the study
that I mentioned originally actually shows that there might be a
greater risk in Business class than economy.