Hematocrits of triathletes: is monitoring useful?

Purpose: The purpose of this manuscript was to provide a basis for establishing safety cutoffs for hematocrit levels in triathletes and background data for possible future medical control regulations. Methods: Competitors from three different distance triathlons participated: Olympic (N = 118), half-Ironman (N = 87), and Ironman (N = 207). Blood samples were drawn within 24-36 h prerace (N = 412) and within minutes of race finish (N = 296). Prerace hematocrits approximated a normal distribution for men (JOURNAL/mespex/04.02/00005768-199903000-00004/ENTITY_OV0398/v/2017-07-20T222656Z/r/image-png = 43.2 ± 2.9) and women (JOURNAL/mespex/04.02/00005768-199903000-00004/ENTITY_OV0398/v/2017-07-20T222656Z/r/image-png = 40.2 ± 2.6). Prerace hematocrits decreased as competitive distance increased for men (JOURNAL/mespex/04.02/00005768-199903000-00004/ENTITY_OV0398/v/2017-07-20T222656Z/r/image-png = 45.0, 43.4, 42.5; respectively; P 0.05). Results: Mean race day changes were small but statistically significant for Olympic and Ironman men and for half-Ironman women. Individual responses were more variable with hemoconcentration occurring in 57%, hemodilution in 43%, and no change in 2% of participants. The magnitude of individual responses was also variable with hematocrit changes ranging from −7.1 to +10%. No athlete in this sample had a hematocrit that would place him/her in the "danger zone" (Hct > 55%). Conclusions: Cutoff values (3 SD above the means) of 52% for men and 48% for women are suggested by these data. However, the relationship of these cutoffs to either athlete safety or the ability to detect rules violations remains unknown.