How It Works

The Athlete Biological Passport (ABP) – known in German as the Biological Passport – works differently from classic doping tests. Instead of searching a single sample for banned substances, the system builds an individual long-term biological profile for each athlete over months and years. Every new measurement is checked statistically against this profile. If a value deviates in a way that cannot plausibly be explained by training, altitude, or illness alone, the system can detect manipulation such as blood doping or anabolic steroid abuse – often without direct proof of a substance.

In cycling, which has been shaped by doping scandals, the Biological Passport has been a central pillar of UCI controls since 2009. The legal framework is provided by the WADA Code; practical implementation takes place through standardized testing procedures and the central ADAMS database system.

Basic Principle: Profile Instead of Single Result

Classic anti-doping tests ask a binary question: Is a banned substance detectable in the sample? The Biological Passport asks a dynamic question: Does the athlete's current biological pattern match their own historical profile and physiologically expected limits?

This paradigm shift is crucial because modern doping methods – especially micro-doses of EPO or autologous blood transfusions – often remain below the detection limit in individual samples. However, they leave characteristic traces in the blood profile over weeks: altered reticulocyte values, atypical hemoglobin curves, or conspicuous OFF-Score fluctuations.

The Two Modules of the Biological Passport

The WADA Biological Passport consists of two independently evaluable modules. Both feed data into the same athlete file but are analyzed with different algorithms and thresholds.

Hematological Module

The hematological module monitors markers of the red blood cell profile. It targets EPO doping, autologous and homologous blood transfusions, and other forms of blood manipulation.

Key measurement parameters:

1. Hemoglobin (Hb) – measures the blood's oxygen transport capacity in grams per liter
2. Hematocrit (Hct) – proportion of red blood cells in total blood volume as a percentage
3. Reticulocyte percentage (RET%) – proportion of young, still maturing red blood cells
4. OFF-Score – mathematically derived index from Hb and reticulocytes; particularly sensitive to short-term manipulation

Typical manipulation pattern: After EPO administration or blood transfusion, Hb/Hct rise while reticulocytes may initially increase and later decrease. The OFF-Score captures such combinations that, viewed in isolation, might still fall within the normal range.

Steroid Module

The steroidal module analyzes hormone and steroid profiles in urine. It targets artificial testosterone administration and manipulated metabolic patterns of anabolic steroids.

Typical analysis points:

• Testosterone and epitestosterone (T/E ratio)
• Long-term metabolites of anabolic steroids
• Isotope ratios to distinguish endogenous vs. synthetic
• Phase profiles across multiple samples

Process: From Sample Collection to Evaluation

The functioning of the Biological Passport follows a standardized chain process that is carried out at every relevant UCI or national control.

Step 1: Whereabouts and Control Planning

Professionals report their location for one hour each morning via ADAMS (Anti-Doping Administration and Management System). Controllers use this data for unannounced tests – particularly important for out-of-competition controls, when doping cycles typically take place.

Step 2: Sample Collection Under Standard Conditions

Blood collection for the Biological Passport follows strict protocols:

• Venous collection by trained personnel
• Immediate labeling with tamper-evident seal
• Documentation of training load, altitude stay, and medication intake
• Transport at controlled temperature to the accredited laboratory

Urine samples for the steroidal module follow analogous chain-of-custody rules.

Step 3: Laboratory Analysis in WADA-Accredited Laboratories

Only laboratories meeting WADA standards may perform ABP-relevant analyses. Results are not viewed in isolation but compared with calibration standards, quality controls, and population reference data.

Step 4: Statistical Evaluation by ABP Software

The ABP software compares each new measurement with three reference frameworks:

1. Individual reference profile – all previous values of the athlete form their personal baseline
2. Population-based thresholds – comparison with reference population of the same discipline and gender
3. Physiological models – expected fluctuations due to altitude training, competition, infection, or dehydration

The system calculates a probability value for relevant parameters indicating whether the observed deviation is natural or caused by manipulation.

Classification of Findings

Not every deviation leads to a doping proceeding. WADA distinguishes graduated finding categories:

With an ABP classification, an independent expert panel (Athlete Passport Management Unit, APMU) reviews the case. The athlete can submit medical explanations – for example for an altitude training camp or a Therapeutic Use Exemption (TUE). If no plausible explanation is provided, a violation of anti-doping rules may be established without a substance ever being directly detected.

The OFF-Score in Detail

The OFF-Score (abbreviation for "OFF-hr" score in hematological evaluation) is one of the most sensitive instruments of the hematological module. It combines hemoglobin and reticulocyte values in a formula designed to detect short-term blood manipulation.

Simplified functional logic:

1. If Hb rises sharply while reticulocytes fall simultaneously, this indicates mature, transfused blood
2. If both values rise sharply in parallel, this may indicate fresh EPO stimulation
3. The OFF-Score combines these patterns into a single alert index

Integration into UCI Controls

The UCI closely links the Biological Passport with other anti-doping measures. WorldTour and ProSeries riders are subject to a minimum control density; top athletes often undergo 20 to 30 tests per season, a significant proportion with blood collection.

Special features during Grand Tours:

• Additional blood tests before and during three-week stage races
• Rest period rules and hotel controls complement the Biological Passport
• No-Needle Policy prohibits injections without medical indication

Practical Examples: How Manipulation Becomes Visible

Blood Doping Scenario

A rider stores their own blood before a Grand Tour and transfuses it during the race:

• Hemoglobin rises above the individual baseline profile
• Reticulocytes initially fall (mature transfused blood)
• OFF-Score exceeds statistical thresholds
• Result: ABP classification, follow-up controls, possible disciplinary proceedings

Limitations of How It Works

The Biological Passport is powerful but not without gaps. The following limitations are established in expert discussion:

• Micro-dosing – extremely small amounts of EPO can remain below the statistical detection threshold
• Profile build-up time – reliable conclusions require multiple samples over months
• Individual variability – rare genetic peculiarities can produce atypical but natural values
• Cost and logistics – blood samples require accredited laboratories and an unbroken cold chain
• Marker dependency – substances without influence on monitored parameters evade the system

Checklist: How It Works from an Athlete's Perspective

Conclusion

The functioning of the Biological Passport is based on long-term profiling, standardized sample chain, WADA laboratory analysis, and statistical pattern recognition. The hematological module with OFF-Score and the steroidal module form two independent monitoring pillars. The graduated classification from Normal through ATU to ABP enables precise responses – from closer controls to disciplinary proceedings.

For professional cyclists, understanding these mechanisms is not a theoretical side issue but a professional foundation: those who know how every blood sample feeds into the statistical overall calculation can consciously manage training, altitude camps, and medical documentation – and thereby contribute to the integrity of a sport striving for restoration of trust.