Hematocrit is the volume occupied by red blood cells (red blood cells or erythrocytes) in the blood relative to the total volume of blood.
The hematocrit level is expressed as a percentage and is measured during a blood test to prevent, diagnose or monitor certain blood abnormalities such as anemia or polycythemia.
Focus on this analysis and on the interpretation of the results of a hematocrit level too low or too high.
What are hematocrit and hematocrit levels?
An important value during a blood test
The hematocrit level is one of the values commonly measured during a blood count, also called a blood test or complete blood count (CBC). Commonly performed, the blood count consists of a quantitative and qualitative analysis of the elements present in the blood including:
- red blood cells also called erythrocytes or more commonly red blood cells;
- leukocytes, better known as white blood cells;
- thrombocytes, which correspond to blood platelets.
An analysis of red blood cells in the blood
Hematocrit is the volume occupied by red blood cells in the blood relative to the total volume of blood. The hematocrit level is expressed as a percentage.
How is the hematocrit level measured?
The measurement of the hematocrit level is done during a blood count. This consists of a blood test. This is usually done in a vein in the arm.
In children and newborns, this blood sample is rather taken on the tip of the finger or at the heel.
Why measure hematocrit levels?
A complementary and essential examination of blood
The hematocrit level is measured in addition to other blood tests including the measurement of red blood cells. By measuring the volume occupied by red blood cells in the volume of whole blood, the hematocrit makes it possible to obtain two other essential blood values:
- The mean corpuscular volume (MCV), which is used to assess the size of red blood cells circulating in the blood;
- the mean corpuscular hemoglobin concentration (MCHC), which is used to assess the mass concentration of red blood cells.
An analysis for the diagnosis or follow-up of certain diseases
In addition to other blood tests, the hematocrit level is used to diagnose certain diseases or to monitor their evolution. In particular, it allows the diagnosis and monitoring of:
- anemia, a blood defect characterized by an abnormal drop in red blood cell levels;
- polycythemia, a blood defect characterized by an abnormally high level of red blood cells
When to measure the hematocrit level?
A preventive control blood count
Like other measurements in a blood count, the hematocrit level can be measured to check for blood abnormalities. These blood tests are essential to diagnose certain abnormalities early and limit the risk of complications.
If anemia is suspected
In addition to measuring red blood cells, hematocrit levels can be measured to confirm the diagnosis of anemia. These measures are usually requested by a doctor when the patient presents:
- generalized fatigue and lack of energy
- muscle weakness
- dizziness and malaise
- shortness of breath
- a pallor.
If polycythemia is suspected
Similar to anemia, a doctor may order a red blood cell and hematocrit measurement to confirm the diagnosis of polycythemia. This is usually manifested by:
- visual disturbances;
- skin redness
- tingling in the fingers;
- itching in contact with water.
In case of dehydration
Hematocrit and red blood cells can also be measured to assess the severity of dehydration. These measurements are usually performed when the patient has:
- intense thirst;
- dry mouth and lips
- lack of sweat and/or urine;
- loss of muscle strength or abnormal fatigue
How to interpret a hematocrit level that is too low or too high?
Analysis of a blood count: how to identify the hematocrit level?
The analysis of a complete blood count takes into account various measurements including the hematocrit level. On the results sheet of a complete blood count, the hematocrit level is identifiable by the abbreviations “Hct” or “Ht”.
Hematocrit level: what are the normal values?
During a blood count, the reference values for the hematocrit level are:
- between 40% and 52% in men;
- between 35% and 47% in women;
- between 32% and 45% in children.
Low hematocrit: what interpretation?
A hematocrit level below the reference values is often a sign of anemia. Characterized by an abnormally low level of red blood cells in the blood, it can have many explanations:
- iron deficiency anemia, which is caused by iron deficiency;
- vitamin B12 deficiency anemia;
- hemorrhagic anemia, which is caused by significant blood loss;
- hemolytic anemia, which is caused by too rapid destruction of red blood cells;
- Aplastic anemia is due to insufficient synthesis of red blood cells.
However, a low hematocrit can have other origins such as sickle cell disease, a genetic disease characterized by an alteration of red blood cells.
During a low hematocrit, the diagnosis requires the analysis of other parameters including the red blood cell rate.
Low hematocrit in pregnant women: what to do?
During pregnancy, many blood parameters change. This is the case of the hematocrit level which tends to decrease. This decrease is explained by an increase in blood volume in pregnant women. This modification is normal and essential for the development of the future baby.
A low hematocrit level in pregnant women, however, requires medical advice, as it can also be a sign of anemia. Due to an increased iron requirement, iron deficiency anemia is particularly common during pregnancy.
High hematocrit: what interpretation?
A hematocrit level above the reference values may be a sign of polycythemia. Characterized by an abnormally high level of red blood cells, it can have several explanations such as:
- Vasquez’s disease;
- certain lung diseases;
- congenital heart disease
A high hematocrit can also be seen during severe dehydration of the body. Other external factors can also cause an increase in hematocrit, including:
- stays at a high altitude.
During a high hematocrit, the diagnosis requires the analysis of other parameters including the red blood cell rate.
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