Become a Member

Get access to more than 30 brands, premium video, exclusive content, events, mapping, and more.

Already have an account? Sign In

Become a Member

Get access to more than 30 brands, premium video, exclusive content, events, mapping, and more.

Already have an account? Sign In



The test that caught Tom Danielson

USADA looks to be applying a much more accurate test to catch dopers that abuse testosterone: Here's how it works.

Don't miss a moment from Paris-Roubaix and Unbound Gravel, to the Giro d’Italia, Tour de France, Vuelta a España, and everything in between when you join Outside+.

It used to be easy to abuse testosterone.

Slap on a patch or spread some topical cream on the skin just after the anti-doping test window closed for the day, at 11 p.m., and levels were all but guaranteed to fall below the threshold for a positive test by the time the window opened up again at 6 a.m.

The positive A sample test of Tom Danielson, 37, admitted doper, claimant of rehabilitation, suggests that such ease of hormonal fraud may have evaporated. The test that found synthetic testosterone in Danielson’s sample is not new, but it is being used in a new way.

Danielson was busted by CIR, short for Carbon Isotope Ratio, a highly accurate test that is able to distinguish between naturally produced testosterone and its synthetic cousin using molecular weight. It is the first test able to detect the synthetic testosterone itself, rather than the body’s reaction to it.

The traditional method of detecting abuse of testosterone looks for an imbalance in the ratio of testosterone and epitestosterone. It is referred to as the T/E ratio test. A normal ratio for most humans is near 1:1. The World Anti-Doping Agency (WADA) considers a ratio over 4:1 to be a positive test. This has dropped in recent years — it was 8:1, then 6:1, and now 4:1. Floyd Landis had a ratio of 11:1 when he was nabbed by both the T/E ratio test and CIR in 2006 with a sample taken during the Tour de France.

If administered at the right time, the T/E ratio method can be very effective. But testosterone/epitestosterone ratios return to normal quickly, even overnight if taken in the right doses. With the ban on overnight testing, which was only recently partially lifted, the test’s real-world efficacy drops considerably.

The T/E test simply looks for a physiological response to doping, rather than the product itself. That is its flaw.

CIR is effective but expensive — $400-700 per sample, nearly 10 times the cost of the T/E ratio test.

Like the T/E test, CIR is also based on a ratio. Labs determine the quantities of carbon-12 and carbon-13, two isotopes, or types, of carbon, within an individual’s testosterone molecules. Synthetic testosterone has less carbon-13 than naturally occurring testosterone.

The ratio between carbon-12 and carbon-13 is constant within an individual. This is the crux of the CIR test: Labs compare the ratio of carbon-12 to carbon-13 in an individual’s testosterone with the carbon-12/carbon-13 ratio in some other, non-performance-enhancing compound, like cholesterol. The two ratios should match. If they don’t, that’s a positive test.

USADA determined that the ratio between carbon-12 and carbon-13 isotopes in Danielson’s testosterone molecules did not match the ratio that occurred naturally in the rest of his body. A synthetic form of the hormone had to be present. How it got there will be the crux of Danielson’s defense, but its presence is undisputed thanks to CIR.

Traditionally, anti-doping agencies used CIR when other intelligence suggested it would return a positive result. That often meant pairing it with the T/E test — run the cheaper version first, and if it produces a suspicious result, bring in CIR for confirmation.

That traditional method, which suffered from the overnight testing loophole, has changed. CIR is now regularly being used independently of the T/E test.

Speaking in the broad terms required until Danielson’s due process reaches a conclusion, a USADA representative confirmed CIR’s independent use, saying, “Not speaking to any athlete specifically, I can tell you that CIR is regularly used and is not used only as a follow-up to T/E ratio.”

The relative inefficacy of the T/E ratio test allowed it to act as a shield for dopers. The T/E test was easy to fool, and that kept CIR off their backs.

On the flipside, the accuracy of CIR does lend itself to the contamination argument Danielson made via Twitter, where he claimed that he would have all his supplements tested. CIR is sensitive enough that it could, in theory, pick up slight contamination. Until USADA releases details of the tests, it’s impossible to know how probable the contamination argument really is.

The fact remains: USADA’s willingness to use CIR without a suspicious T/E result changes the game. The overnight test ban, as porous as it now is, is no longer any protection against a positive for testosterone. A gaping loophole in anti-doping testing has been closed.