I'm not sure if anyone saw this, but its pretty straight forward; its
also one of the better articles Velonews has pub'ed:
The Hamilton Case: A doctor explains blood doping
By Shannon Sovndal, M.D.
This report filed September 28, 2004
How times change. Just last week, EPO was the talk of the town. Now
you can't open the sports page without reading something about
transfusion blood doping. Sport doping is going old school. Out with
the new, in with the old.
Blood transfusions have long been used to enhance athletic
performance. Transfusions are an extremely straightforward, simple,
and effective method of increasing the blood's oxygen carrying
capacity. Physiologists believe that it is the rate at which
hemoglobin delivers oxygen to the exercising muscle that limits muscle
performance. Blood transfusions address this limitation by increasing
the number of hemoglobin molecules carrying oxygen to the muscles.
The term "blood doping" refers to various techniques used to increase
the oxygen carrying capacity of blood. Recently, recombinant human
erythropoietin, more commonly known as "EPO", has been the drug of
choice. However, with the advent of more effective and inclusive
testing, the use of EPO has become more difficult and complex.
Because of the increased risk of detection, there has been concern
that athletes may turn to an older form of blood doping that, until
recently, has been virtually undetectable. This basic performance
enhancing use of blood transfusions is at the center of the recent
doping controversy involving rider Tyler Hamilton.
Homologous versus autologous
There are two methods of doping through blood transfusions: autologous
and homologous. With an autologous transfusion, an athlete receives
his or her own blood. An athlete donates blood, stores it, and then
receives the blood at a later point in time. The advantages of this
technique are the avoidance of diseases such as HIV or hepatitis, the
reduction of the risk of detection through testing, and the
alleviation of potentially deadly transfusion reactions.
The downside of autologous doping is that it takes time for the body
to recover from the loss of blood that occurs during donation. It
would be hard to train effectively while having to donate a supply of
blood sufficient to enhance performance. In a homologous transfusion,
the blood comes from another person. The benefit of homologous
transfusion is no decrease in performance during the donation period.
However, the disadvantages are the risk of contracting blood born
diseases, the risk of transfusion reactions, and increased transfusion
sensitivity.
Homologous transfusion is now the focal point of the current doping
controversy. All individuals have a specific and consistent
genetically programmed blood type. Each blood cell in the body has
markers or antigens that hang off the cells. These specific antigens
determine an individual's blood type. The major blood types are A, B,
and O. The positive or negative value added to the ABO type refers to
another antigen on the blood cell called Rh(d). If you have both the A
antigen and the Rh(d) antigen, your blood type is A positive. In
addition to these major antigens, there are numerous other "lesser"
antigens that make up each person's blood composition. It is possible
to test not only for one's major blood type (A+ or O-, for instance)
but also for the lesser antigens on one's blood cell. By this test, we
can define even more specifically the makeup of an individual's blood.
Markers
Researchers have now applied this test to the war on doping. A
scientific paper written by Nelson, et al., and published in the
journal Haematologica explains the new test in more detail. But,
because of the subject matter, the article gets a bit technical. I
will try to explain the test using as little medical jargon as
possible.
Every red blood cell has a consistent and specific set of blood group
antigens. When these antigens are tagged with fluorescent dyes, a
machine known as a flow cytometer can differentiate cells with
different sets of antigens. Based on the blood being tested, a certain
set of antigens is marked, and the cells are placed in the flow
cytometer.
A large number of cells, 50,000-60,000, are shuffled into a
single-file line and moved through a detection tube. A laser
illuminates the fluorescent tags and sensors sort the cells depending
on which antigens light up. The machine produces a graphical picture
of the findings, and for any individual person, a single spike
representing their inherent antigen set appears on the paper. If a
person has received even a small amount of homologous transfused
blood, a second, smaller spike representing another antigen set also
appears, and the test is "positive" for doping.
This procedure may sound complex and fraught with errors, but flow
cytometry is nothing new to medicine or science and has been used for
a long time with accurate results in many applications.
Does it work?
The research study mentioned above tested the process on 25 patients
and was 100-percent accurate. Still, many question the validity and
applicability of the test. Should the group of test subjects be
larger? Should the test subjects be elite cyclists? Should a large
sample of people not receiving transfusions be tested to look for
false positives? (A false positive occurs when the test reads
positive, but the athlete has not been doping.)
The answer to all these questions would seem to be yes. However, in
defense of the test, flow cytometry does work. Hundreds of athletes
have been tested using this technique and only a few positives have
been found. It is also possible that additional research was completed
internally by the drug testing organization prior to the test's use.
It would seem that at the very least, this test is a good screening
test.
While a screening test is extremely good at catching all individuals
doping, it does run the risk of having false positives. The next step
in a thorough investigation would be a confirmatory test. This mirrors
the procedure for HIV testing in the hospital. If the screening test
is positive for HIV, a second, more specific test is completed to
confirm the diagnosis.
Confirmation?
The problem is, there is no easy confirmatory test. A first thought is
to evaluate the blood sample for a DNA. Every person has a totally
unique DNA program that can be differentiated from every other person.
However, testing a blood sample with only a small fraction of
homologous blood could be tricky. If, by chance, the sample used for
the test didn't contain the donated blood, the result would show only
the DNA of the tested individual.
This is called preferential amplification. There are tests available
that can avoid this problem, but they are complicated and pricey. Many
of these methods have certainly been tested in the field of
criminology, but as evidenced by the OJ Simpson case, a definitive and
convincing answer is often elusive.
Before these tests could be used to prove doping occurred, research
studies would need to be performed specifically addressing this
situation. A simpler suggestion, but by no means foolproof, would be
to repeat the flow cytometry test again at a later date. Red blood
cells have a lifespan of 120 days. If the test is run at 60, 90, and
120 days, the transfused red blood cells should slowly disappear,
leaving only the athlete's cells on the test. The only way to keep
these cells from diminishing would be to continue to transfuse the
exact same blood supply the athlete previously received. It is
plausible the athlete could do this, but it would be complicated,
especially during the scrutiny of an investigation.
Athletes these days are often put through the ringer by the drug
testing agencies. Their lives are disrupted frequently, even if they
never test positive. Since a positive test will likely ruin an
athlete's career, there should be no doubt when delivering a positive
test verdict. I have long been a fan of cycling, and am sorry to
continually read about new doping scandals. I never thought I'd need
my medical degree just to figure out the technology behind the latest
and greatest doping techniques.
Over the years I have learned to trust the scientific method and
analyze the research data with as little bias as possible. However, in
this case, as a longtime fan of Tyler Hamilton, I hope the available
data is incorrectly pointing to a conclusion that is ultimately
untrue.
References
Nelson et. al "Proof of homologous blood transfusion through
quantification of blood group antigens." Haematologica, vol. 88(11):
November 2003
Cram, Scott. "Flow cytometry, an overview." Methods in Cell Science,
24: 1-9: 2002
Alvarez et. al "Relative sensitivity of direct antiglobulin test,
antibody's elution and flow cytometry in the serologic diagnosis of
immune hemolytic transfusion reactions." Haematologica, vol 85(2):
February 2000