EPO: What We Know, And What We Don’t, About The Blood-Doping Threat

When Lance Armstrong confessed in 2013 to taking Epogen to boost production of oxygen-carrying red blood cells, horse racing fans began looking behind every tree for the boogeyman called erythropoietin, or EPO. Many had long suspected EPO had risen to prominence in horse racing in the 1990s alongside anabolic steroids, and news that one of cycling's biggest stars was using it seemed to cement the idea it could be lurking anywhere – even at the top levels of the sport.

Thanks in part to Armstrong, many people have a basic idea of how EPO works. EPO is produced naturally by the kidneys of all mammals and signals the bone marrow to make more red blood cells. More red blood cells mean increased hemoglobin, which is responsible for carrying oxygen. In the 1980s, a man-made version of EPO (recombinant EPO) was developed as a treatment for anemic patients who could not circulate enough EPO to keep their red blood cells at a safe level. Today, FDA-approved forms of EPO for humans include Epogen, Aranesp, Retacrit, and Procrit. When given to healthy people, however, the synthetic EPO boosts red blood cells to higher-than-normal levels, allowing athletes better endurance.

Most racing insiders who have some idea of what EPO does also know that it has been favored by human athletes in part because it's difficult to test for. Like anabolic steroids, EPO's competitive advantage lies in its ability to boost the body's natural production of certain materials, but unlike anabolics, the drug itself disappears from the body quickly. One set of instructions written by a still-practicing veterinarian and provided to the Paulick Report in 2015 suggested the drug was given in repeated injected doses, often along with iron, for maximum effectiveness.

The first tests for EPO were developed in the early 2000s — so where do we stand now in our ability to catch trainers engaging in blood doping? And what's on the horizon for both cheaters and regulators?

The modern testing process

Currently, getting an EPO positive (and there have been a few over the years) is a two-step process. Testing laboratories use an ELISA kit test to screen for it and then forward a split sample to a more advanced lab, which performs mass spectronomy testing to confirm. The confirmation testing is a multi-day procedure that must be performed by technicians with specialized advanced training.

Dr. Richard Sams, former laboratory director at LGC Sport Science Lab in Lexington, Ky., said the ELISA kit test used for screening was based on detecting human EPO, which is most of what seems to be available on the market. The good news is he believes the ELISA kit could detect all types of human EPO commercially available. The bad news is, it focuses on human EPO.

All mammals make EPO naturally, and roughly 80 percent of the molecule is the same between horses and humans. Since EPO is incredibly expensive to produce and buy, it stood to reason cheaters would focus on giving to horses human EPO developed for sale to human athletes. (And yes, there are a number of dubious online outlets which claim to sell EPO or EPO-like products to horsemen, but these outlets are not regulated closely and there's a significant chance the products aren't what they claim to be.)

In Sams' time at LGC, the lab's home base in Fordham, England, was responsible for EPO confirmation for the Kentucky lab (and a number of others). About two years ago, Sams recalled a smattering of tests with suspicious ELISA kit results which came back as no-confirmation from Fordham.

“We [the Lexington lab] and Fordham routinely discussed findings, and the Fordham scientists who were responsible for confirmation analysis told us about the same time that we began sending these suspicious samples over that weren't confirmed, they were getting similar samples from other labs that could not be confirmed,” Sams recalled.

Because of the chemical construction of human EPO, it must have three particular peptides on its sequence to come up on both ELISA kit and confirmation analysis. (Naturally produced EPO in horses has always been different enough that it doesn't produce a positive on either test, so there's no fear of a horse's own EPO causing an accidental positive.) Sams could only suppose someone had begun using a type of EPO that was similar enough to human EPO to flag one test without fulfilling the other — perhaps EPO derived from another species. There have been no new forms of EPO approved for therapeutic use in humans in recent years, so whatever it is, it's not coming through a Food and Drug Administration-approved channel, which raises its own questions about product safety. We still don't know what product caused those unconfirmed tests, or where it came from.

“I'd be surprised if anything was made clandestinely for the racing market, but there may very well have been something made clandestinely for human athletic competition,” said Sams.

It's understood that some drugs, such as dermorphin, can be edited in their chemical makeup to evade tests. Sams said he doesn't worry about that so much with EPO.

“It would be exceedingly difficult,” he said. “I think the bigger risk is making horse EPO or presumably you could use other kinds of EPO that are different from human and horse which produce an EPO-like effect. Any time you would switch from one EPO to another, the labs would have to develop a new test.”

What are the risks?

Administering EPO of any sort to a horse also comes with risk. Although human EPO molecules are 80 percent identical to horse EPO, that last 20 percent can set off alarm bells in the equine body. Some horses recognize the substance as a foreign invader and begin producing antibodies to attack it. In some cases, the immune response can be so severe that the horse's body also begins producing antibodies to its own EPO, resulting in anemia. Anemia isn't particularly common in fit, healthy horses but if it's left untreated, it can be a long, slow death.

And what about the rumored use of poisons and other blood thinners to counteract overenthusiastic EPO administration? EPO use in humans is believed to sometimes result in blood which has become too thick from hematocrit, resulting in circulation problems. Hematocrit is the ratio of red blood cells to total blood volume.

Railbirds have long theorized positive tests for blood-thinning agents may be explained by some attempt on the part of trainers or veterinarians to balance out the effects of blood doping. There's one problem with that, Sams said: Horses have contractile spleens, which store large amounts of red blood cells and release them at times of stimulation, such as the start of a race or as part of a startle response. When this happens, the hematocrit rises significantly. The equine body has obviously figured out how to cope without encountering circulation issues, though we don't know how exactly. (This is one more reason detection is difficult – testing can't conclude for sure if a horse's hematocrit level is high because of a recent spleen contraction or because of an EPO administration – at least, not yet.)

Because we don't know how the equine body may deal with elevated hematocrit, we don't know whether those blood-thinners are given intentionally to horses receiving EPO, or whether they're safe or effective.

How common is EPO use?

Without a better way to detect EPO, we really don't know how commonly it may be given to racehorses. The ELISA kit test used by laboratories these days can detect recent administrations of the drug, but anyone looking to boost performance would need to give EPO and then wait several weeks for it to take full effect – at which time it's long gone from the bloodstream. Post-race testing is not likely to encounter it, although Sams knew of a few instances where it was found in post-race samples from harness racing in Maine, likely due to the frequency of races for that population.

Dr. Mary Scollay, equine medical director for the Kentucky Horse Racing Commission, said she has no idea how common it really is, but she does get questions about it.

“We certainly hear about it,” she said. “It has been detected in a couple of cases in recent history. There are people who believe its use is profligate and others who say 'I don't think so.' And I can't answer the question.”

Dr. Mark Cheney, board member of the Kentucky Equine Drug Research Council (KEDRC), suspects the use has become more common than people want to believe. Cheney has been outspoken in meetings of the KEDRC over the effectiveness of EPO testing more so than any other performance-enhancing substance. Cheney is also disturbed by the volume of distributors marketing EPO-like products on the Internet.

“It is, I would say, just about epidemic use in our industry,” he said in an Oct. 2, 2018, meeting of the KEDRC. “Some trainers, I'm not going to mention any names, their horses are just rebreaking at the eighth pole.

“We're never going to be able to test for these products … if we have just an inkling of research to show we can identify someone that's using an epogenic product, as soon as you put that on the front page of the Lexington Herald-Leader, they'll stop using it. There's probably some pretty important people in this business that have done it.”

What do we do about it?

Given the low likelihood of finding EPO in a post-race test, experts say there are two ways its use can be curbed. The easier and quicker of the two options is increased out-of-competition testing (OOCT). Many – but not all — states have rule language allowing OOCT, though having rules permitting it and having the funding for extra laboratory tests are two separate issues.

Sams points out that in some jurisdictions where OOCT is common, it's not a good idea to make its scheduling too predictable. In many cases, trainers may learn how far out from a race the OOCT sample will be collected and administer long-acting performance-enhancing drugs like EPO immediately after the sample has been taken. Sams suggests regulators take OOCT samples and return in two to three days to take another set. EPO can be detectable for an average of two to four days after administration, up to a week in some cases.

The more effective form of testing is still far off. There is ongoing research into the creation of equine biological passports. They look for unusual changes in proteins or other biomarkers in the blood in response to drugs like EPO or anabolic steroids, which produce artificial levels of natural cells.

“Biological passports have been used very successfully in human testing to detect EPO,” said Sams. “It does not work in horses for a number of reasons, one of which is the ability of the horse to store red blood cells in the spleen and the ability to then release them. We don't see a lot of stability in hematocrit and hemoglobin because the horse can release those red blood cells when it's being handled before the blood sample is collected.”

Reticulocytes are another key giveaway in human biological passports — they act as a type of signal that a new round of red blood cells are being made. Horses don't produce them as part of this process.

The Racing Medication and Testing Consortium recently funded two studies to improve detection of EPO, which executive director Dr. Dionne Benson hopes will result in tenfold or greater detection sensitivity.

In 2018, the Kentucky Equine Drug Research Council gave funding to an ongoing project from the lab of Dr. Scott Stanley to explore biological passports for horses. Earlier this year, the group provided a grant to Dr. Heather Knych of the University of California-Davis to look at changes in gene expression following microdosing of EPO. Scollay hopes the work could lead to a new type of monitoring.

“I think this potentially provides an investigative tool to run some facts against the speculation,” said Scollay. “It is not a standalone enforcement tool. It would identify a sample for a confirmatory analysis for EPO. You don't hang your hat on a screening test, but on the other hand, there's nothing wrong with a screening test triggering some information gathering.”

If successful, Knych's research cannot tell a regulator that a horse has gotten EPO, only that its results are out of the ordinary and it may be helpful to do more investigation.

“I would definitely say that this is only a first step,” Knych echoed.

There's another challenge with EPO detection from biological passports — in Kentucky and probably elsewhere: Scollay has raised concerns about the phrasing of Kentucky's rules. They prohibit the finding of “a drug, medication or substance” and “substances present in the horse in excess of concentrations at which the substances could occur naturally.”

Biomarkers don't fit into either category.

“Right now, our regulations require the unequivocal identification of a molecule in the horse to determine it carried that prohibited substance,” Scollay said at an October meeting of the Kentucky Equine Drug Research Council. “I'm not sure how the attorneys across the country, or in Lexington, are going to feel about prosecuting a case based on indirect evidence of a substance having been in the horse at some point. I know USADA is able to do some of that, but we're government agencies as opposed to a sports club.

“I think we're in the early stages of this; there's an awful lot to learn about this substance in the horse.”