Hematocrits of triathletes: is monitoring useful?

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.

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 (X = 43.2 +/- 2.9) and women (X = 40.2+/-2.6). Prerace hematocrits decreased as competitive distance increased for men (X = 45.0, 43.4, 42.5; respectively; P < 0.01) but not for women (P > 0.05).

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%).

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.