What is HCT? What are the situations in which hematocrit value changes?

Hematocrit HTC: Red blood cells called erythrocytes are responsible for the transmission of oxygen passing through the lungs to other tissues and organs in the body. In addition to oxygen, it also takes part in the transport of carbon dioxide molecules. Erythrocytes take the carbon dioxide formed as a result of using oxygen as a result of the cells’ metabolism, carry them to the lungs, and allow them to be discharged.

Red blood cells (erythrocytes) are produced in the bone marrow. They are formed by the division of stem cells in the bone marrow. Certain substances and hormones are necessary for the production of erythrocytes. Examples include erythropoietin, vitamin B12, folic acid, and iron mineral.

While there are approximately 4.8 million red blood cells in women per cubic millimeter of blood, this figure is approximately 5.4 million for men.

The transport of oxygen and carbon dioxide is due to the hemoglobin contained in red blood cells. Since hemoglobin is a molecule containing iron, it causes the blood to appear red. Disc-shaped red blood cells do not have a core.

What is the hematocrit(HCT)?

It refers to the ratio of the volume of red blood cells to the amount of circulating blood.

Mathematically, it is calculated by multiplying the average red blood cell volume (MCV) measured with the aid of the instruments and the number of thyroid cells. Normal hematocrit values ​​are accepted between 35-45%.

Hematocrit value is one of the parameters included in the complete blood count test. The most common reason for examination is anemia. In the report containing the test results, the hematocrit is briefly expressed as “Hct”

What is HCT? What are the situations in which hematocrit value changes?

How is hematocrit measured(HCT)?

(HCT) Hematocrit measurement is performed with a glass tube and centrifuge device. The working principle of the centrifuge device is based on the separation of the mixed substances by using the difference in density. The container containing the mixture rotates at high speed and the heavier substance is pushed towards the outside of the container, thus ensuring separation.

While centrifugation is taking place, other cells in the bloodstream may remain among the red blood cells. This situation may cause the hematocrit value to be measured higher than normal.

The volume of red blood cells may increase as a result of waiting a long time for the blood sample to be examined. In this case, the hematocrit value can be calculated higher than its true value.

What are the situations in which the hematocrit value changes?

In many physiological conditions, it may cause the hematocrit value to be calculated below or above normal limit values.

The hematocrit (HCT) values ​​of babies in the neonatal period are high and decrease to normal levels over time. There are also differences between genders in terms of hematocrit (HCT) value, and higher values ​​are detected in men than in women.

In women during pregnancy, lower hematocrit values ​​can be detected due to the increase in the amount of blood in circulation and the decrease in its density.

In people living in high-altitude areas, the number of red blood cells increases in order to balance the lack of oxygen in the air. Therefore, the hematocrit values ​​of those living in high-altitude areas can be determined above the normal range.

Since the number of red blood cells in the bloodstream is proportional to the hematocrit value, the hematocrit (HCT) is found to be low when the number of red blood cells decreases.

Anemia (anemia)

A decrease in the number of red blood cells called erythrocytes in the bloodstream due to various reasons is called anemia. This reduction may be due to slowing production or increased destruction.

Weakness, headache, difficulty concentrating, feeling cold in hands and feet, shortness of breath, and dizziness are examples of symptoms that may occur in anemia.

Iron deficiency anemia is one of the most common causes of anemia. Iron is necessary for the production of red blood cells as it is included in the structure of the hemoglobin molecule. Deficiency may occur during pregnancy when excessive tea drinking, grain-based diet, or iron need is higher.

Blood losses are also naturally a cause of anemia. While responding to rapid blood losses, it is aimed to replace the fluid volume in the circulation first. Therefore, while the amount of fluid reaches normal levels, the number of red blood cells, and thus their concentration decreases. The decrease in hematocrit values ​​after blood loss returns to the normal value range within approximately 1-1.5 months.

Anemia may also occur as a result of the disorders in the bone marrow, which is the production site of red blood cells. This type of anemia due to insufficient production is called “aplastic anemia”.

As a result of the deficiency of substances such as vitamin B12 and folic acid, which are necessary for the production of red blood cells, the production in the bone marrow slows down and the cells produced are detected as larger than normal. This type of anemia is called “megaloblastic anemia”.

Vitamin B12 taken with food becomes absorbable from the intestines through a factor (intrinsic factor) secreted from the stomach and is transported to the necessary areas in the body for use in various events. In this condition, which is called pernicious anemia, a decrease in vitamin B12 absorption occurs due to the production of this factor, which is secreted from the stomach and allows the absorption of vitamin B12, and thus the production of red blood cells is negatively affected.

The lifetime of erythrocytes is approximately 120 days. Red blood cells, which carry out the duty of carrying oxygen and carbon dioxide during this period, are broken down by the spleen when their life is completed, and the molecules they contain are returned to the bloodstream to be used in the synthesis of new cells. In the presence of various congenital abnormalities in the structure of red blood cells, their destruction occurs in a shorter time. This anemia condition, where destruction increases according to production, is known as “hemolytic anemia”.


The situations in which the total fluid volume in the blood circulation is lost for various reasons and insufficient fluid intake occurs are called dehydration. As the amount of fluid decreases, the number of red blood cells does not change, and the hematocrit value can be detected as relatively high. This condition, which is called hemoconcentration, can also occur after burns, after excessive vomiting, and after the formation of obstruction in the intestines, apart from dehydration.

As a result of heavy exercises, the hematocrit value can be detected as high.


It refers to the red blood cell count being above its normal values. It may occur in the absence of sufficient oxygen, or it may occur during the course of malignant diseases that cause uncontrolled proliferation in the bone marrow.

If the reason for the increase in cell number occurs in response to another situation, it is classified as secondary (secondary), if it is directly related to the increase in production, it is classified as primary (primary) polycythemia.

Among the causes of secondary polycythemia, living in high altitudes and situations such as heart failure can be given as examples where cells and tissues cannot get enough oxygen.

“Polycythemia Vera”, a disease characterized by excessive blood cell production as a result of mutations in stem cells in the bone marrow, is one of the primary causes of polycythemia.

Normally, the number of red blood cells varies between 3.5-5.5 million per cubic millimeter, while the number can rise up to 7-8 million cells during this disease. Hematocrit value can be determined as 60-70%. After this increase in the number of cells in circulation, the fluidity of the blood also decreases.

Almost 4 out of 5 patients do not have any complaints during the diagnosis of the disease. Patients with complaints usually complain of symptoms such as weakness, headache, or itching after a warm shower.

Lung disorders

Smokers and people with chronic obstructive pulmonary disease (COPD) have a chronic (long-term) oxygen deficiency and therefore the measured hematocrit values ​​may be higher than normal.

At the same time, the change in the fluidity of the blood with the increase in the hematocrit value may cause the development of resistance in the vessels distant to the heart, causing people with high hematocrit values ​​to have high blood pressure values ​​at the same time.

The page content is for informational purposes only. Items containing information about therapeutic health services are not included in the content of the page. Consult your physician for diagnosis and treatment.

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Billett HH. Hemoglobin and Hematocrit. In: Walker HK, Hall WD, Hurst JW, editors. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Boston: Butterworths; 1990. Chapter 151. (https://www.ncbi.nlm.nih.gov/books/NBK259/Accessed 2/13/2018.

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