The Athlete Biological Passport (ABP) is principally founded on monitoring an athlete's biological variables over time, to identify abnormal biases on a longitudinal basis. Several factors are known to influence the results of these markers. However, the manner in which the altitude factor is taken into account still needs to be standardized. Causal relationships between haematological variables should be correctly integrated into ABP software. In particular, modifications of haematological parameters during and after exposure to different altitudes/hypoxic protocols need to be properly included within detection models. Copyright © 2013 John Wiley & Sons, Ltd.