In the late 1990s, Dr. Don Catlin was the first to develop and offer the carbon isotope ratio, or CIR, test to determine whether testosterone or an anabolic steroid has been made naturally by the body or has come from a prohibited substance. This highly accurate test was the first technique capable of detecting synthetic testosterone, rather than simply gauging the body’s reaction to the substance. Dr. Catlin used for comparison a person’s endogenous reference compound (ERC) such as cholesterol to help determine the body’s natural carbon make-up. The CIR test was considered revolutionary and has proven useful and highly reliable; despite many challenges by athletes testing positive over the years, the Court of Arbitration for Sport has never found any fault with it.
See an info-graph about his test put together in 2006 for the New York Times: https://www.nytimes.com/imagepages/2006/08/01/sports/02landis-graphic.html
Catlin DH, Hatton CK, Starcevic S. Issues in detecting xenobiotic anabolic steroids and testosterone by analysis of athletes’ urine. Clinical Chemistry 1997;43:1280-1288.
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