Gastrointestinal Symptoms, Fluid Loss and Haematological Parameters

Response to Professor Banfi's Letter to the Editor:

We thank Professor Banfi for his thoughtful comments on our pilot study. The main outcome of our research was that the adaptive model used for the Athletes Biological Passport (ABP) will not flag athletes that are victims of severe fluid loss consecutive to gastrointestinal distress. For this purpose, we presented blood data from 5 athletes obtained at various time points before, during and after periods of severe gastroenteritis. No treatment (intravenous fluid replacement or other) was administered before the blood sampling. None of the athletes had values outside the limits calculated by the ABP model. Further, none of the athletes showed significant haemoconcentration despite the severity of the symptoms that made the athletes seek medical help in our outpatient department.

Professor Banfi states in his letter that “severe episodes of diarrhoea and/or vomiting, that commonly affect professional athletes during competition, can lead to increased haemoglobin concentration”. Interestingly, in an extensive literature research, we did not find any scientific evidence for this, at first glance, very logic and appealing assumption. As mentioned above, none of the 5 athletes in our study showed a significant increase in Haemoglobin concentration. In our manuscript, we describe a theory on why this apparently clear phenomenon is not visible: Of all fluid compartments of the human organism, the plasma volume/blood volume entity is the most “protected” in pathological conditions and will be kept constant even during severe fluid loss to preserve organ function. Several investigations confirming this theory are referenced in our article. On the other hand, as correctly pointed out by Professor Banfi, plasma volume plays a major role in the adaptation to endurance exercise in physiological conditions, as shown in many studies (“Sports Anaemia”). These apparently contradicting regulations highlight the complexity of the human plasma volume regulation.

Professor Banfi emphasizes the importance of confounding factors that might influence the results of the adaptive model to the disadvantage of the athlete (standardisation of sampling conditions, posture, competitive season, type of sports, exercise, amount of fluid loss etc.). In the presented cases that lack any standardisation by WADA principles with regard to the above and thus represent “worst case” conditions for the athlete, none of our subjects failed the limits set by the adaptive model.

The timing of the samples was not standardised in the present athletes and therefore mimics the conditions in Anti Doping Routine, where sampling is not performed in strict intervals. In all cases presented here, several months had elapsed between the routine samples and the samples obtained during the gastrointestinal episodes. The adaptive model calculates individual “thresholds” at defined specificities (in our study 99.9% abnormality was chosen). After the first value, the model takes previous values of the same athlete in consideration to adapt the individual thresholds. For the first value in each profile, only population references are used, as no values from the same athlete are available at this point. These averages can differ between sports (as can be seen in our athletes 1 and 2 (soccer) and 3–5 (cycling)).

In summary, we feel that the points raised by Professor Banfi deserve full academic consideration in the evaluation of blood values in athletes, but, in the context of our study, do not affect the results and the key message of our research.

Correspondence