Variability of Hematic Parameters

How big should the variation of Hb or Hct be in an athlete in order to be able to affirm that the values of that parameter have significantly changed? 

The critical difference (dK) is defined as the entity of the variation required in successive measurements in one individual to affirm that the hematic parameter really modified. 

dK90 is the critical difference measured on the 90th percentile, meaning it can be referred to 90% of the population. This means that 10% of the subjects can manifest bigger variations without these being significant change. 

Costongs & Co. (J. Clin. Chem. Clin. Biochem., 1985; 23: 69-76) noticed a dK90 of 14-15% for Hb and Hct, either for measurements in the same day or in successive days, as well as 6 months later (measurements done in the same laboratory and in standard conditions). 

This means that we should notice Hb variations of about 2g% or Hct variations of 8 points in order to suspect that something intervened in the modification of those parameters. 
Inferior variations can be identified as physiologic oscillations of Hb and Hct.
Without forgetting that 10% of the subjects are excluded from this statistic valuation, and can show bigger variations without significant change. 

Costongs’ study evaluated 274 healthy subjects, in standard conditions, without intercurrent pathologies, but not athletes. 
For active athletes it is logic to expect even bigger dK due to training effects in both plasma volume (PV) and red cells volume (RCV). 
The influence of PV and RCV on Hb and Hct concentrations is well known. 

Three weeks of training are in fact sufficient to obtain an increase by 500 ml in PV and 280ml in RCV (Eur. J. Appl. Physiol., 1988; 57: 490-498). 

In elite athletes (Int. J. Sports Med., 2005; 26: 350-355) traditional altitude training for the duration of 3 weeks at 2050m determined an increase in the total hemoglobin volume (tHb) from 14.0 to 15.3 g/kg (increase by 9.2%), as well as in RCV from 38.9 to 43.5 ml/kg (increase by 11.8%). 
The schedule “live high-train low” (J. Appl. Physiol., 2006; 100: 1938-1945) for 24 days confirms similar increases in tHb (+5.4%) and RCV (+4.9%). 

Retrospective studies on elite athletes between the years 1978 and 1987 (when EPO was not available and manipulations/dilutions were not necessary…) demonstrated Hct values that were 50% higher in about 10% of the examined samples during the racing period. 
During the winter period such percentage was up to 18% (Int. J. Sports. Med., 1999; 20: S21). 

All the recent studies after 1997, year that saw the introduction of hematic tests in cycling and nordic skiing, cannot exclude the possibility that the involved athletes could have altered the measurements, lowering Hb and Hct concentrations by taking adequate fluid quantities so to come up with “normal values”. 

Also the Australian “ON-score” and “OFF-score” formulas are a result of statistic valuations that do not exclude the possibility of errors, with “false positives”. 

Australian researchers who developed and proposed these formulas haven’t so far been subject to any critical valuation to their work from scientists who were not involved in the political-economical business of the “fight against doping”. 

The same authors have nonetheless admitted that CAUTION must be taken when valuating the hematic results of athletes who have recently been exposed to natural or simulated altitude (Haematologica, 2003; 88: 1053-1062). 

There is little if none scientific literature concerning the dK of reticulocytes in athletes, which should nonetheless be decisively big, considering the short life (2-4 days) of these cells that quickly grow to adult red blood cells. 
Simple training determines an increase in reticulocytes (Eur. J. Appl. Physiol., 1988; 57: 490-498) as well as the exposition to natural or simulated altitude.