The title of Watson and Maughan’s article (7) in this issue of Medicine and Science in Sports and Exercise ® suggests a method article focusing only on laboratory analytical techniques. However, this article provides very useful, applied information for sport drug-testing agencies (e.g., World Anti-Doping Agency), athletes, and coaches. As the authors clearly state (page 53), presample conditions such as dehydration, exercise, and fluid intake are not standardized during doping control testing. Because all of these conditions alter plasma osmolality, this article (7) is relevant to both laboratory science and sport performance, in a variety of ways.
First, because several authors have demonstrated an inverse relationship between the size of red blood cell and plasma osmolality (1,2,4), and increased plasma osmolality during dehydration (5), this investigation (7) stands on the shoulders of classic studies that inform our understanding of assessing extracellular fluid shifts during exercise. For example, David L. Costill investigated a similar question with Bill Fink in the 1970s. They realized that a Coulter counter suspends red blood cells in a saline solution, altering erythrocyte volume. Costill et al. (1) evaluated the influence of osmolality by using diluents ranging from 249 to 346 mOsmol·kg−1. Also in 1974, Costill teamed with D.B. Dill of the Harvard Fatigue Laboratory to recommend that both hematocrit and hemoglobin be incorporated into the calculation of plasma volume shifts because hemoglobin concentration was unaffected by changes in plasma osmolality. Their joint publication of this method (3) today stands as one of the most highly referenced articles in the history of exercise science, with more than 2200 journal article citations (6).
Second, previous studies incorporated automated hematology analyzers without benefit of the present data. This likely means that the effects of standard isotonic solutions and preprogrammed instrument dilutions on osmolality were not considered, yet Watson and Maughan’s article (7) illustrates that this is an important distinction. Thus, previous publications should be reevaluated to determine whether they distinguished between manual and automated hematology analyzer measurements of hematocrit because they assessed the factors that influence plasma volume shifts (i.e., exercise intensity, postural change, heat exposure).
Third, it is widely recognized that athletes use diuretics as masking agents to avoid positive drug tests, via increased total body water turnover. We do not know, however, which athletes, if any, have manipulated plasma osmolality to avoid detection of erythropoietin use or autologous erythrocyte reinfusion. The answer to this question is worthy of future investigation.
Finally, Watson and Maughan’s article (7) is relevant to the laboratory as well as the playing field because (a) regression-derived lines of best fit (their Figs. 1 and 3) provide models for laboratory technicians if plasma osmolality is known or can be estimated, (b) the findings emphasize careful consideration of automated processes and underlying physiological principles, and (c) the fact that conditions (i.e., eating, drinking, hydration status, exercise) are not controlled before athlete doping tests represents a call for procedural change.
Lawrence E. Armstrong, PhD
Human Performance Laboratory
University of Connecticut
Department of Kinesiology
1. Costill DL, Branam L, Eddy D, Fink W. Alterations in red cell volume following exercise and dehydration. J Appl Physiol. 1974; 37 (6): 912–6.
2. Costill DL, Fink WJ. Plasma volume changes following exercise and thermal dehydration. J Appl Physiol. 1974; 37 (4): 521–5.
3. Dill DB, Costill DL. Calculation of percentage changes in volumes of blood, plasma, and red cells in dehydration. J Appl Physiol. 1974; 37 (2): 247–8.
4. Harrison MH. Effects of thermal stress and exercise on blood volume in humans. Physiol Rev. 1985; 65 (1): 149–209.
5. Senay LC, Christensen ML. Changes in blood plasma during progressive dehydration. J Appl Physiol. 1974; 37: 247–8.
6. Web of Knowledge Web site [Internet]. Thomson Reuters [cited 2013 Jul 16]. Available from: www.webofknowledge.com
7. Watson P, Maughan RJ. Artifacts in plasma volume change due to hematology analyzer-derived hematocrit. Med Sci Sports Exerc. 2014; 46 (1): 52–9.