What is it
The hematocrit (distinguished by the acronym HCT) expresses the relationship between the corpuscular part of the blood, consisting mainly of red blood cells (and, to a lesser extent, white blood cells, also called leukocytes, and platelets) and the liquid part of the blood, or plasma.
Hematocrit is an index expressed through a percentage. For example, a hematocrit value of 45% means that there are 45 ml of red blood cells in 100 ml of blood.
How to measure
To measure hematocrit, venous sampling is required. The blood sample is usually taken from a vein in the arm, but can also be collected by a puncture of the finger or heel, as is the case with young children.
The test tube containing the sample is then taken to an analysis laboratory and centrifuged by means of automated instruments, obtaining a clear separation between the red blood cells, which are deposited on the bottom, and the plasma that overhangs them. The hematocrit expresses the percentage amount of cells piled up on the bottom.
What are the normal values
Normal values, in addition to being slightly higher in men than in women, may vary depending on several factors, such as age, pregnancy and altitude. For example, during pregnancy, as delivery approaches, hematocrit levels are reduced, while blood becomes more fluid. At high altitudes, however, the opposite happens: the number of red blood cells increases to cope with the scarcity of oxygen present in the atmosphere, and the blood becomes thicker and more viscous.
Here are the reference values:
| Men | 42-52% |
| Women | 37-47% |
| Pregnant women | 30-47% |
| Residents in high-altitude areas | 45-61% (men)
41-56% (women) |
| Infants | 55-68% |
| Children of 1 year | 29-41% |
| Children of 10 years | 36-40%. |
When it is prescribed
When you do a general check to assess your health, or you are in the presence of symptoms such as tiredness, fatigue, dizziness, headache and weakness, hematocrit is one of the first tests to be prescribed.
This is a routine test, usually performed together with the analysis of the concentration of hemoglobin in the blood (the Hgb) or as part of the blood count (the most common and complete blood test, also known as a blood count).
The test can also be used to evaluate and monitor certain conditions that involve changes in red blood cells, such as anemia (a decrease in the number of red blood cells in the blood) or polycythemia vera (a neoplasm of the hematopoietic cells of the bone marrow), as well as to assess the hydration status of the body.
High hematocrit
When the hematocrit is high it means that there is an increase in the amount of blood cells: especially red blood cells (or erythrocytes), but also white blood cells (leukocytes) and platelets (essential for blood clotting).
Theblood is therefore made denser, more viscous and flows with greater difficulty, which can have repercussions on the heart, which has more difficulty pumping it to send it into circulation.
In some cases, blood struggles to reach the smallest vessels, resulting in decreased blood flow to certain areas of the body (a condition known as hyperviscosity syndrome).
In addition, the higher density of the blood determines the increase of platelets and favors the formation of clots, which can in turn cause serious cardiovascular events such as heart attack or stroke.
There are several conditions associated with hematocrit values above normal. These include:
- dehydration,
- erythrocytosis,
- polycythemia (divided into primary polycythemia and secondary polycythemia),
- acute renal failure,
- certain lung diseases,
- and live at high altitudes.
If you sweat too much, use diuretic drugs or in the presence of conditions that involve vomiting and diarrhea, you may experience dehydration, which causes a reduction in the liquid part of the blood (represented by 90% water), thus increasing the ratio between red blood cells and plasma and, consequently, also the hematocrit values. In these cases the number of red blood cells does not rise, but the plasma quota decreases.
On the contrary, in the case of polycythemia, the hematocrit is high because there is an increase in red blood cells, while the plasma component remains unchanged. Possible symptoms of polycythemia are vision disorders, dizziness, headache, red color of the face, etc.
Finally, even the intake of drugs containing doping substances, such as erythropoietin, can increase hematocrit values; Reason why the hematocrit test is included in the anti-doping tests to which athletes and sportsmen who compete at a competitive level are regularly subjected.
Low hematocrit
There are many reasons why the hematocrit value can be low. They range from anemia to bleeding, from prolonged aerobic training to chronic renal failure.
Possible causes are also:
- certain deficiency defects (such as, for example, those of vitamin B12, B9 and B6),
- defects in hemoglobin synthesis,
- the reduction of erythropoiesis (the process of red blood cell production), associated with chronic inflammation and autoimmune diseases.
For example, in the case of bleeding, excessive blood loss also results in a loss of red blood cells, greater than the production of new red blood cells, causing symptoms such as dizziness (when it is fast) or tiredness, wheezing and pallor (when it is gradual).
On the other hand, in the case of iron deficiency anemia (caused by iron deficiency), since hemoglobin is low, the share of red blood cells decreases and consequently so does the hematocrit. Classic spy symptoms are fatigue and fatigue, pallor and wheezing.
Joycelyn Elders is the author and creator of EmpowerEssence, a health and wellness blog. Elders is a respected public health advocate and pediatrician dedicated to promoting general health and well-being.
The blog covers a wide range of topics related to health and wellness, with articles organized into several categories.