Q: What is synthetic human growth hormone (HGH)?
A: A banned, performance enhancing drug that is hard to detect and has been linked to health problems such as diabetes, cardiac dysfunction and arthritis.
Q: How does the NFL's blood test to detect synthetic HGH work?
A: The body naturally produces several types of growth hormone, which weigh less than synthetic HGH. To try to detect the use of the banned HGH, the NFL uses what is called the isoform test, which measures the ratio of the different types of growth hormone - those produced by the body, and one that can be produced both by the body and synthetically. If someone is using synthetic HGH, that latter part of the ratio increases.
Q: How many players are tested during the season?
A: Each week, 40 out of the league's more than 1,600 players get checked for HGH - five players on each of eight teams, randomly selected by computer.
Q: How does a player know if he's been picked for an in-season test?
A: A piece of paper gets taped to his locker, telling him he needs to have blood drawn.
Q: Then what happens?
A: A player has to head to a testing room at the team facility, where no more than 15 milliliters of blood (less than a tablespoon) will be drawn. The blood is shipped to an accredited lab and split into two samples, which are tested using separate kits. If either of those samples tests positive, another sample from the same blood draw is also tested, using the same kit, for confirmation.
Q: Why not check urine for HGH, the way the NFL tests for other drug use?
A: The byproducts of HGH are so scant in urine that it isn't considered a feasible way to detect its use.
Q: Because they're world-class athletes, is there a chance a professional football player could produce more growth hormone than the average person?
A: Yes. But the test doesn't measure the amount of growth hormone; it measures a ratio. Years of science have proven that the typical ratio of synthetic growth hormones to the other growth hormones in the non-doping population is about 0.8, no matter what a person's body type.
Q: But there are always outliers, aren't there? Could a player who tests positive just be someone who naturally has an elevated level of growth hormone?
A: That's why the test's designers allowed for a substantial margin of error. According to scientists, the conservative ''decision limits'' - the ratios someone would have to hit to test positive - give the average athlete a better chance of being struck by lightning than falsely testing positive. In 2013, for example, of the 2,798 HGH tests processed at labs accredited by the World Anti-Doping Agency in 2013, none produced a positive result.
Q: How long is the window of detection for the isoform test to pick up synthetic HGH in someone's system?
A: About 48 hours.
Q: Does such a short time span make it easier to avoid detection?
A: Yes. The agreement between the league and the players' union doesn't allow blood draws on game days; the league did refuse to eliminate the possibility of a test the day before a game because of the short detection window.
Q: Are there any other HGH blood tests available?
A: A new one, called the biomarkers test, has been scientifically validated and is expected to be widely available in the next few months - but the union would have to allow its use. It measures byproducts the body produces when a person takes synthetic growth hormone, and is supposed to be able to detect HGH use for up to three weeks; it cannot detect it in the first 48 hours or so. So the thinking is that this new way to check for HGH would be used to supplement the isoform test. The current agreement between the NFL and union says the isoform test will be used ''unless and until the parties agree on use of another testing methodology.''
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