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Hematocrit in Athletes - State Of The Art
By: Michele Ferrari
Published: 24 Apr 2003

The following is an article that Dr. Ferrari wrote about hematocrit: it is a summary of concepts taken from several scientific resources (see the bibliography at the bottom) and personal comments from Michele Ferrari himself.

The hematocrit (HCT) is an extremely variable clinical parameter, and many factors can modify its levels.

It has been known for some time that posture has a measurable effect: standing erect augments HCT levels by as much as 10% over the supine position (9, 27, 33), in the same way that variations in body inclination cause changes in plasmatic volumes (PV) and therefore HCT (30).
From this we can deduce that sitting for long periods, as in long car or plane trips, can significantly change HCT levels.

Various stress situations also modify hematocrit levels.

- An intense effort, even brief (12, 13, 14, 15, 32) will cause increases in HCT (+5 - 10%) probably because of the increase in blood pressure, with a consequent change in Starling balance and PV reduction. Periods of emotional intensity or fear can have the same effect.

- A prolonged effort, like a bike race or marathon, can cause very significant variations in PV and HCT in the hours and days following the effort (10,37,39). A multi-stage bike race, or intense and repeated training sessions will cause measurable transitory HCT changes (38): this shows that HCT can be affected by the training sessions and/or races of days preceding the measurement.

- Exposure to heat (27, 31, 32) produces a strong reduction of PV, with consequent increase in HCT, due to dehydration

- Acute exposure to cold (28) reduces PV and increases HCT because of the increase of peripheral resistances and thus of blood pressure. Simple cooling of skin temperature causes hemo-concentration (36) with an increase in HCT.

Athletes in training have a Red Cell Mass (RCV) 15% higher than control groups (10, 20), as well as a 19-20% increase in PV, depending upon the specific sport engaged in (20, 22). Since the PV increase is higher than the RCV increase, the hematocrit levels in these athletes is somewhat lower than that of control groups (20, 21, 34).

Three weeks of training on a cycloergometer (a home trainer), at five sessions per week and only 45 minutes a day were enough to produce an average increase in PV of 420 ml and an increase in RCV of 280 ml, with measurable changes in HCT (40).

A suspension of training (detraining, due to sickness, accident, travel or other reasons) can cause an increase in HCT of between 4 and 8% in only a few days (10, 11, 21). Since athletes have increased RCV (20), a sudden interruption of training can cause higher than “normal” HCT levels.

HCT levels, like haemoglobin concentration, can vary in a single subject by as much as 15%, depending upon the time measurements are taken (41, 42, 43).

Prolonged application of a tourniquet also increases HCT: three minutes of application raises HCT by 3.9 points (9). Also, the diameter of the needle used, and the position of the needle inside the vein (set against the vein wall or positioned in the center of the vein) can also have an effect on the HCT level measurements.

Hematocrit measurements with automatic utensils (like a Coulter Counter) are vulnerable to error, especially in relation to the equipment’s calibration which is not generally renewed daily and which is not always carried out using a standard for high values.

Retrospective studies show high levels of HCT of over 50% in 10% of well trained athletes (29, 44, 45).

Populations living at high altitude show much higher levels, even more than 60% hematocrit in people living above 4000 meters (1, 2, 19, 23). Similar levels are shown in Europeans who stay at such an altitude for prolonged periods (3). A group of Italian helicopter pilots measured by Cerretelli (3) showed an average HCT level of 55%.

These observations show that our genetic code and our bodies have the possibility of adapting and functioning with hematocrit levels much higher than 50%. Natural production of EPO increases during a stay at altitude by 3-10 times, depending upon the altitude (4, 5, 16), and in only few hours reach concentrations in the blood far higher than measured in healthy subjects who have taken doses of pharmaceutical synthetic EPO under medical supervision (6, 24, 25). In certain severe forms of anaemia, the plasmatic concentration of EPO can exceed normal concentration by 100 times (7, 26).

It has been shown that HCT levels above 50%, blood viscosity increases considerably: this may be true in vitro, but it may not correspond to what actually happens within the variable systems of our vascular apparatus; nor do we fully understand which compensatory mechanisms our bodies are capable of putting into action (7, 8).

Hematocrit is therefore useful and usable as indicator of the athlete’s health, and to limit the risk of “abuse” - pharmaceutical or otherwise.

But this measurement cannot be used alone as a proof of doping, because it is too vulnerable to outside influences and factors that have nothing to do with doping.

- Bibliography -

1) J. APPL. PHYSIOL. , 51(6): 1411-1416, 1981
2) RESPIRATION PHYSIOLOGY, 61: 197-208, 1985
3) MANUALE DI FISIOLOGIA DELLO SPORT E DEL LAVORO MUSCOLARE, di Paolo Cerretelli. Soc. Ed. Universo, Roma, 1990. Pag. 409
4) AM. J. PHYSIOL. , 266: R756-R764, 1994
5) J. APPL. PHYSIOL. , 59(2): 360-364, 1985
6) MED. SCI. SPORTS EXERC. , 27(11): 1569-1576, 1995
7) HEMATOLOGY, 5th Ed. Williams. McGraw-Hill. Pag. 445-446
8) BLOOD, 31(3): 332-343, 1968
9) LA TRASFUSIONE DEL SANGUE IN MEDICINA CLINICA, di P.L. Mollison, Ed. Piccin. Pag 82-83
10) EUR. J. APPL.PHYSIOL. , 63 : 463-466, 1991
11) J. APPL. PHYSIOL. , 60(1) : 95-99, 1986
12) MED. SCI. SPORTS EXERC. , 31(6): 800-808, 1999
13) MED. SCI. SPORTS EXERC. , 22(2): 250-256, 1990
14) EUR. J. APPL. PHYSIOL. , 58: 53-61, 1988
15) J. APPL. PHYSIOL. , 87(1): 175-182, 1999
16) J. APPL. PHYSIOL. , 75(4): 1696-1701, 1993
17) J. APPL. PHYSIOL. , 32(1): 54-58, 1972
18) J. APPL. PHYSIOL. , 68(3): 1186-1194, 1990
19) J. APPL. PHYSIOL. , 66(4): 1561-1569, 1989
20) EUR. J. APPL. PHYSIOL. , 79: 244-250, 1999
21) J. APPL. PHYSIOL. , 48(4) : 665-669, 1980
22) INT. J. SPORTS MED. , 20: 149-153, 1999
23) BLOOD, 33(5): 668-676, 1969
24) MED. SCI. SPORTS EXERC. , 31(5): 639-645, 1999
25) BR. J. CLIN. PHARMACOL. , 42: 355-364, 1996
26) EUR. J. CLIN.INVEST. , 19 : 117-127, 1989
27) EUR. J. APPL. PHYSIOL. , 80: 1-8, 1999
28) EUR. J. APPL. PHYSIOL. , 64: 244-249, 1992
29) INT. J. SPORTS. MED. , 36th German Congress of Sports Medicine and Prevention, 1999; 20 sup. 1: A-069 e A-074, 1999
30) J. APPL. PHYSIOL. , 78(4) : 1369-1373, 1995
31) J. APPL. PHYSIOL. , 57(4) : 1018-1023, 1984
32) J. APPL. PHYSIOL. , 37(4) : 521-525, 1974
33) J. APPL. PHYSIOL. , 45(3) : 414-418, 1978
34) INT. J. SPORTS. MED. , 36th German Congress of Sports Medicine and Prevention, 1999; 20 sup. 1: A-067, 1999
35) EUR. J. APPL. PHYSIOL. ,, 80: 353-359, 1999
36) J. APPL. PHYSIOL. , 54(2): 515-523, 1983
37) EUR. J. APPL. PHYSIOL. , 73: 49-55, 1996
38) MED. SCI. SPORTS EXERC. , 31(5): S324 n° 1623, 1999
39) MED. SCI. SPORTS EXERC. , 22(5) : 581-587, 1990
40) EUR. J. APPL. PHYSIOL. , 57: 490-498, 1988
41) BRIT. J. HAEMAT. , 3: 117-123, 1957
42) AM. J. CLIN. PATHOL. , 69: 48-54, 1977
43) J. CLIN. CHEM. CLIN.BIOCHEM. , 69-76, 1985
44) INT. J. SPORTS. MED. , 20: 538-541, 1999
45) INT. J. SPORTS. MED. , 21: 380-385, 2000



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