How valid is the determination of hematocrit values to detect blood manipulations?

The aim of this paper is a critical reflection of the practice in competiti ve cycling to use the hematocrit value (Hct) as an indirect control measure for doping with erythropoietin. To demonstrate the individual physiologica l variation of Hct values, five different studies were performed: 1. Eight subjects were observed (i) during 23 h after a 1 h lasting bout of cycle ex ercise at 60 % of maximum performance and (ii) during 24 h under control co nditions. 2. Seven subjects were exposed to a 20 min period of -7 degrees h ead down tilt (HDT), which was followed by 15 min in sitting position. 3. F rom four subjects blood samples were taken in a sitting position up to 60 m in after they had ingested 1 liter isotonic saline solution. 4. Ten subject s performed a vita maxima test on a cycle ergometer, starting at 100 W and increasing the workload by 17 W every minute. 5. Four elite cyclists partic ipated in a 10 days competition (1700 km). Results: 1. During the 24 h obse rvation period Hct decreased during the night from 45.3 +/- 3.1 % to 42.9 /- 1.5 % and returned to the initial values in the morning. This diurnal va riation was even more pronounced after submaximal exercise (-4.1 %). 2. Due to fluid shifts from the interstitial into the intravasal compartment, HDT was accompanied by a 3.1 +/- 0.5 % lower Hct. 3. Drinking of the isotonic saline solution also reduced the hematocrit by 3.3 +/- 0.5 % after one hour . 4. Maximum cycle exercise increased the Her from 46.8 +/- 2.4 % to 51.3 /- 1.9 % which was due to a 15 % decrease in plasma volume. 5. Repeated bou ts of cycle-exercise reduced the Hct from 46.4 +/- 1.5 % to 41.3 +/- 1.6 %, Conclusions: All experiments demonstrate that the Ha is not a constant val ue but can be considerably changed by physiological measures. Clinical stud ies show that brain oxygen supply decreases with increasing Hct-values, whi ch are also associated with a higher risk of stroke accidents. We therefore recommend to use a Hct-limit solely under strongly controlled standardized conditions, to protect professional cyclists from hazardous manoeuvre unti l more appropriate methods to detect EPO-doping are developed.