Hematocrit: how to interpret a low or high rate?

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Hematocrit: how to interpret a low or high rate?

What is hematocrit?

First thing to know: when a blood test is performed, a complete blood count is systematically carried out, ie a complete blood test that examines white blood cells, red blood cells and platelets. " This is one of the basic exams that assesses the health status of an individual "explains Dr. François Blanchecotte, Doctor of Pharmacy and President of the National Union of Biologists (SDB).

Thehematocrit is one of them: this measurement makes it possible to evaluate the proportion of red blood cells in the total volume of the blood. " Today, we do this with advanced machines, develops Dr. Blanchecotte. But in the old days, a little blood was put in a test tube, the red blood cells were allowed to pile up at the bottom, and the volume of the red blood cells was measured in relation to the total volume. "

The hematocrit is therefore expressed as a percentage: " in a woman of about 30 years, a normal hematocrit is included between 35% and 45%explains Dr. Blanchecotte. In a man, he will be between 40% and 55%. And in a baby, the hematocrit will be understood between 50% and 60% ".

How to explain this difference between men and women? " Schematically, we can say that women have less blood than men, and that the red blood cells of men are bigger "explains the specialist.

Warning : " hematocrit is not a measure that can be interpreted alone. It must be related to two other parameters: the total number of red blood cells and the rate ofhemoglobin ".

Hematocrit too low: what can be the causes?

" Obviously, as soon as one loses blood (in case ofhaemorrhage internal or external haemorrhage), the hematocrit will drop since there will be a loss of red blood cells "says Dr. Blanchecotte.

Two other situations can also lead to a decrease in the proportion of red blood cells in the blood:

  • A hemodilution : " this can happen in the hospital, when the patients are perfused with saline: the blood is too diluted and this leads to a fall of the hematocrit "explains the specialist.
  • A anemia : it can be caused by certain pathologies (rheumatoid arthritis, Crohn's disease, renal insufficiency, leukemia ...), by an unbalanced diet (major deficiency of vitamin B12 or vitamin B9, for example) or by a disorder of the cord bone (in the case of aplastic anemia, the production of blood cells is greatly diminished).

Good to know : It should be noted that in case of pregnancy, the hematocrit appears to be lower since the plasma volume increases.

Hematocrit too high: what can be the causes?

" In high-level sportsmen, too high a hematocrit can reveal a case of doping since a higher concentration of blood in red blood cells leads to better oxygenation of the muscles, therefore better sports performance explains Dr. Blanchecotte.

An abnormally large proportion of red blood cells can also be observed in other situations:

  • Hemochromatosis is a pathology that is characterized by excessive intestinal absorption of iron and a significant production of red blood cells. This disease affects, in France, 1 person out of 200 to 1 person out of 1000 according to the regions: Brittany and Gard would be more concerned.
  • " After one blood transfusion following a surgical procedure (for example, the installation of a total hip prosthesis), a high hematocrit "adds the specialist.
  • In case of dehydration, because the volume of plasma decreases, the concentration of red blood cells in the blood seems higher.

Thanks to Dr. François Blanchecotte, Doctor of Pharmacy and President of National Union of Biologists (SDB).

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