How Does Doping Testing Work? Samples, Thresholds and the Athlete Biological Passport

The World Anti-Doping Agency, established in 1999 after a cycling scandal made the previous patchwork untenable, publishes a Prohibited List that is revised annually and adopted by sports federations and national bodies. A substance goes on the list if it meets two of three criteria: it enhances performance, it poses a health risk, or it violates the spirit of sport, a phrase that does a great deal of undefined work. Some substances are banned at all times, including anabolic steroids, growth hormone, blood boosters such as erythropoietin and masking agents; others only in competition, including stimulants, narcotics and cannabinoids, which is why an athlete can legally use certain drugs in training and not on race day. Methods are banned as well as substances, notably blood transfusion and any manipulation of a sample. Athletes with a genuine medical need can apply for a therapeutic use exemption, a process whose transparency has itself been a source of argument.

The chain of custody is the point of the entire procedure, since a result is worthless if the sample could have been swapped:

• •Athletes in a registered testing pool must file their location for every day, including a sixty-minute window each day when they can be found, and three missed tests or filing failures in twelve months is itself a violation
• •Testing is both in competition, usually of the top finishers plus random selections, and out of competition with no notice at all, which is where most meaningful detection occurs
• •A chaperone stays with the athlete from notification to collection, and urine collection is directly observed to prevent substitution
• •The sample is split into an A bottle and a B bottle, both sealed by the athlete, and only the A is analysed unless it returns a finding, in which case the athlete may demand the B be opened in their presence
• •Blood samples are taken for tests that urine cannot do, including growth hormone and the markers used in the biological passport
• •Analysis takes place only in laboratories accredited by the agency, currently about thirty worldwide, and samples are stored frozen for up to ten years for later reanalysis

Most detection uses mass spectrometry coupled to gas or liquid chromatography, which separates the compounds in a sample and identifies each by its mass and fragmentation pattern, and the sensitivity is extraordinary, reaching picograms per millilitre. The hard cases are substances the body makes itself. Testosterone administration is detected not by its presence but by ratios, originally the ratio of testosterone to epitestosterone and now more reliably by carbon isotope ratio mass spectrometry, which distinguishes synthetic testosterone made from plant sterols from the body's own by the proportion of carbon-13, a difference of a few parts per thousand that cannot be disguised. Erythropoietin is separated from the natural hormone by differences in its sugar attachments, using a gel that pulls the two apart by charge. Blood transfusion of someone else's blood is found by detecting two populations of red cells; transfusion of the athlete's own stored blood leaves no foreign marker at all, which is why an indirect approach was needed.

The most significant change since 2008 is a shift from looking for the drug to looking for its effects. The Athlete Biological Passport records selected blood and steroid markers over years, establishing each athlete's individual baseline and the normal variation around it, and then flags statistically improbable departures from that personal range rather than from a population threshold. A sudden rise in reticulocytes followed by a fall, or a haemoglobin level that moves in a pattern training cannot explain, indicates blood manipulation without identifying any substance. The method catches what direct testing misses, including transfusions and microdosing schedules designed to clear before a test, and it can support a sanction on its own. Its weakness is that it requires many samples over time, expert panel review, and an athlete who is actually in a testing programme, none of which is universal.

Several limitations are structural rather than fixable by better chemistry. Detection windows are short for many substances, and an athlete with expert advice can time a cycle to clear; the East German and later Russian programmes showed that a state-backed system can defeat testing entirely by controlling the laboratory, which is what the Moscow laboratory did by swapping sealed bottles through a hole in a wall during the 2014 Winter Olympics. Designer steroids can be synthesised specifically to be invisible to existing assays, as the substance at the centre of the BALCO case in 2003 was, and was found only because a coach posted a syringe of it to the authorities anonymously. Coverage is wildly uneven across countries and sports, and testing is expensive, so most athletes in most sports are rarely or never tested. Against that, the stored-sample reanalysis programme has stripped medals from dozens of competitors years after the event, and the deterrent value of knowing a sample from today may be analysed with a technique invented in 2032 is probably larger than any single test.

A global agency publishes the banned list, and detection rests on no-notice out-of-competition testing, a strict chain of custody with split A and B samples, and analysis in about thirty accredited laboratories using mass spectrometry. Substances the body makes itself are caught by ratios and carbon isotope analysis, and since 2008 the biological passport has tracked each athlete's own blood markers over years to flag improbable changes without identifying any drug. The system is defeated by state control of laboratories, designer compounds and uneven coverage, and countered partly by reanalysing stored samples for a decade.