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Not medical advice. The Atlas is not a substitute for a clinician who can examine you.

The Athlete Biological Passport and Testosterone Testing

T/E Ratio, the Steroidal Module, and Carbon-Isotope (IRMS) Confirmation

Evidence grade 5 of 5, Settled. Read how the Atlas grades evidence.

The written rationale for this grade is still being prepared.

FDA
Not an FDA matter; WADA-accredited laboratory methods
WADA
Detection framework for S1 Anabolic Agents

Reference only. Not medical advice.

What can go wrong

For athletes, the system is powerful: even microdosed testosterone can perturb the longitudinal steroid profile and trigger IRMS confirmation. For clinicians and patients, the lesson is that endogenous-looking labs do not equal anti-doping clearance, and that the biology of detection is more sophisticated than a single number.

This is something to take to a clinician. The Atlas can tell you what is known about the athlete biological passport and testosterone testing in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.

Detecting exogenous testosterone is hard because the body makes testosterone naturally. Anti-doping science solves this two ways. The steroidal module of the Athlete Biological Passport (ABP), launched in 2014, tracks each athlete's urinary steroid markers, most notably the testosterone-to-epitestosterone (T/E) ratio, longitudinally, flagging atypical shifts. Suspect samples then go to gas chromatography/combustion/isotope-ratio mass spectrometry (GC/C/IRMS), which can distinguish naturally produced testosterone from pharmaceutical testosterone by its carbon-isotope signature.

How testers catch the molecule your body also makes, by tracking ratios over time and reading carbon isotopes.

What people take it for

What it is taken for. Approval, where it exists, covers only some of these.

  • Longitudinal monitoring of an athlete's own baseline
  • Flagging atypical steroid profiles for follow-up
  • Confirming synthetic vs endogenous testosterone origin

How it works

Epitestosterone is an inert isomer the body produces in roughly 1:1 ratio with testosterone. Exogenous testosterone raises T without raising epitestosterone, pushing the T/E ratio up. Because individuals vary, the ABP compares each athlete to their own established baseline rather than a single population cutoff. When a profile looks atypical, GC/C/IRMS measures the carbon-13/carbon-12 ratio of the steroid: pharmaceutical testosterone, derived from plant sterols, carries a distinct, depleted carbon-isotope signature versus testosterone the body synthesizes from dietary carbon.

Why a normal T/E does not mean clean

A genetic deletion in the UGT2B17 gene reduces testosterone glucuronidation, so some athletes (notably of East Asian ancestry) have very low baseline T/E and can dope while staying under a fixed ratio threshold. This is precisely why the ABP shifted from a single 4:1 cutoff toward individualized longitudinal monitoring, and why IRMS carbon-isotope confirmation, which does not depend on the ratio, is the decisive test.

What people get wrong

  • Often saidBody-identical testosterone is undetectable

    ActuallyGC/C/IRMS reads the carbon-isotope signature of pharmaceutical testosterone, which differs from endogenous testosterone regardless of how 'bioidentical' it is.

  • Often saidStaying under a 4:1 T/E ratio means you pass

    ActuallyIndividualized passport monitoring and IRMS can flag doping even when a fixed ratio looks normal.

Who profits, and who pushes back

Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.

At a glance

ABP steroidal module launched
2014
Key marker
Urinary T/E ratio
T/E flag threshold
Atypical above ~4 (lowered to 4 in 2004)
Confirmation method
GC/C/IRMS (carbon-isotope ratio)
Serum markers added
Testosterone and androstenedione, 2023

What this entry does not yet cover

What follows is unfinished work on our side, not a finding about The Athlete Biological Passport and Testosterone Testing. A short entry is not a safe entry.

  • Timeline. We have not built the dated record of research and regulatory events.
  • Cost and market. We have not documented what it sells for or who sells it.
  • Supply chain. We have not mapped where it is made.
  • Who uses it. We have not documented the user groups.
  • What could change. No forward-looking summary yet.
  • How it compares. We have not set it against the alternatives.
  • Children and teenagers. We have not checked what is known about younger people.

Sources

The studies below are named and described, but not linked. You cannot open them from here and check our reading against them, which means this page is our summary of the literature rather than a document you can verify. Weigh it accordingly until the links exist.

The studies that matter

  • WADA lowers T/E threshold to 42004

    Tightened the screening cutoff for atypical steroid profiles

  • Steroidal module of the ABP launched2014

    Enabled longitudinal monitoring of urinary steroid markers

  • UGT2B17 deletion and T/E sensitivity2015

    Showed gene deletion lowers baseline T/E, motivating individualized profiling and IRMS

  • Serum T and androstenedione added to ABP2023

    Extended the steroidal module to blood markers