High and Low Hematocrit Levels

Importance of observing High and Low Hematocrit Levels

High Hematocrit Levels and Low Hematocrit Levels occur due to alternations in the volume of packed Red Blood Cells of human blood. I have previously spoken about the Normal Hematocrit Levels and mentioned that Hct levels are normally decreased by aging. Hematocrit levels are very associated with Red Blood Cells count and Hemoglobin Levels.


The Hematocrit test is usually ordered by doctors in addition to the Hemoglobin Levels (Hgb) and Red Blood Cells Count tests to help the physician to have a full picture of how healthy are the the Red Blood Cells of the patient. Hematocrit levels are the percentage of packed red blood cells height inside a centrifuged blood tube. In other words, the Hematocrit level is a measurement of the Red Blood Cells volume and it is helpful to determine if the RBCs size is normal or not and if the Red Blood Cells Count is normal or not. Hematicorit Levels are used with RBC Count and Hemoglobin Levels to calculate the Mean Corpuscular Volume (MCV) and Mean Corpuscular Hemoglobin Concentration (MCHC) respectively. Both MCV and MCHC are Red Blood Cell Indices which are used to classify Anemia.


Normally, the Hematocrit Level in terms of percentage equals to 3 times the Hemoglobin level in terms of grams per deciliter (g/dl) when the person has normal Red Blood Cells size. For example, a person with Hematocrit level of %30 would normally have an approximate Hemoglobin concentration level of 10g/dl. Alternations to this relationship are obvious indications of abnormal Red Blood Cells sizes. For example, a case of %50 Hematocrit level and 10g/dl Hemoglobin concentration would be diagnosed as a case of abnormally large Red Blood Cells.

Normal, High, and Low Hematocrit Levels

Normal, High, and Low Hematocrit Levels as they appear inside a Centrifuged Blood Tube


High and Low Hematocrit Levels can be caused by normal factors

Hematocrit levels are very close and affected by alternations in Hemoglobin concentration (Hgb) and Red Blood Cells Count (RBC Count). The following is a listing of the reasons that may cause normal alternations to the Hematocrit levels; it is the physician responsibility to be sure that alternations to the Hematocrit levels aren’t caused by those natural causes before jumping into conclusion that those alternations are caused by any diseases:

–          Pregnancy; during pregnancy, several physiological changes occur including a chronic state of over-hydration which cause the total blood volume to increase and lower down the relative volume of the packed Red Blood Cells which is the measurement of the Hematocrit levels leading to Low Hematocrit Levels.


–         Hydration; Hematocrit level is typically affected by hydration level. Hydration raises the plasma level in the blood, causing the relative volume of Hematocrit to be decreased due to over-hydration or increased because of dehydration. While the Hematocrit level is affected by hydration, the patient is not required to fast for the Hct test to be done.


–          People who live on high elevation normally have high Red Blood Cells count because of the decreased amounts of oxygen in air at high altitudes. Human body normally attempts to increase the oxygen supply to the different body tissues by increasing the production of Red Blood Cells and hemoglobin to overcome the possibility that the current number of Red Blood Cells is not enough to supply enough oxygen. The increased production of Red Blood Cells would cause an increase of the packed RBC volume causing a High Hematocrit Level.


Causes of High Hematocrit Levels

  • Increased size of Red Blood Cells causes an increase in Hematocrit Level. Since Hematocrit Level is the percentage volume of Red Blood Cells, abnormally big Red Blood Cells will increase the volume of packed RBCs and the Hematocrit level as well. The increase of Red Blood Cells can be diagnosed if the Hematocrit Level is more than 3 times the Hemoglobin level.
  • Erythrocytosis; Erythrocytoc is defined as the increase in Red Blood Cells count that is caused due to physiological response to external stimulations rather than hematogenic systemic disorder. An example of Erythocytosis is increase of RBC count due to  living in high altitude.
  • Severe Dehydration reduces the volume of plasma in the blood which causes the total blood volume to be reduced. As a matter of fact,  Severe Dehydration doesn’t raise or even impact the total Red Blood Cells count, instead, the resulting reduction of the blood volume increases the relative volume of the packed Red Blood Cells causing High Hematocrit levels.
  • Polycythemia Vera is a myeloproliferative blood condition that occurs when the bone marrow produces excessively enormous quantities of Red Blood Cells which causes increased volume of the packed Red Blood Cells and noticeable High Hematocrit Levels.
  • Cyanotic Heart Defects are a collection of Congenital (Birth) Heart Defects that cause the patient skin color to have a bluish or cyan color (be Cyanotic).  Cyanotic Heart Defects occur because the blood which travels through the lungs and entering the systemic circulation to access the other body organs to be deoxygenated causing levels oxygen potential pressure (pO2) to be decreased. As a result; the human body generates huge numbers of Red Blood Cells as physiological response to low pO2 level caused by the Cyanotic Heart Defects. The High RBC count will be seen as High Hematocrit level inside a centrifuged blood tube.
  • Chronic Obstructive Pulmonary Disease (COPD); This disorder causes the airways of  the respiratory system to be shrunk overtime causing insufficient oxygen supplies to the body members. In advanced cases of COPD, the body produces more Red Blood Cells causing High Hematocrit Levels.

Causes of Low Hematocrit Levels:

Patients that has low Hematocrit Levels may require blood transfusion only if they have a low Hemoglobin level and they are in a health condition that doesn’t enable them to produce sufficient Red Blood Cells in a short period of time.


The transfusion decision is taken by doctors considering age, health condition, Hematocrit Level, and Hemoglobin Level. For example, a young person with a Hemoglobin level of %8 and capable of increasing his or her cardiac output (the volume of blood that could be pumped by the heart) safely may not require transfusion at Hematocrit level of %18 while an older person who had issues with oxygen carrying capacity may require transfusion at a Hematocrit level of %28 or higher.


Causes of Low Hematocrit Levels need to be identified and resolved with caution since it can be a life threatening condition if sufficient amounts of oxygen cannot be delivered to the different body members. These causes include:

  • Pregnancy naturally causes several physiological changes to the pregnant female body. These changes include a chronic condition of overhydration which cause the total blood volume to raise and lower down the Red Blood Cells ratio in the blood which can be seen as  Low Hematocrit Level inside a centrifuged blood tube.
  • Anemia is defined as the reduction of Red Blood Cells count. There are several types of diseases that associate with and cause Anemia. The Low Red Blood Cells count that characterizes Anemia is accompanied with Low Hematocrit Levels.
  • Hemoglobinopathy is the reduction of Hemoglobin concentration in the blood caused by a Hemoglobin disorder or any other blood diseases that reduce the Red Blood Cells count or reduce the life span of Red Blood Cells and this consequently leads to Low Hematocrit Levels.
  •  Cirrhosis is the condition of fluid preservation and overload that is caused by chronic liver disease. The fluid excess causes the Red Blood Cells to be diluted and cause a low ratio of the total blood volume and Low Hematocrit Levels as an outcome.
  •  Hemolytic Anemia is a condition that occurs when Red Blood Cells breakdown abnormally causing a shorter life span for the Red Blood Cells. The Red Blood Cells breakdown decreases the RBC count, and consequently causes Low Hematocrit Levels.
  • Dietary Deficiency:  The deficiencies of vitamins ( Vitamin B12 for example) or minerals (specifically Iron) that are necessary in the production of Red Blood Cells, Also problems with digesting or absorbing those necessary vitamins and minerals will cause delivering fewer or small size Red Blodd Cells and causing  a noticeable Low Hematocrit Level.
  • Bone Marrow Failure causes decreased production of the various types of blood cells including the Red Blood Cells, this leads to low Red Blood Cells count and Low Hematocrit Levels.
  • Prosthetic Heart Valves lead to a mechanical trauma to the Red Blood Cells which reduces the Red Blood Cells life span and, consequently, the RBC count will be decreased causing Low hematocrit Levels.
  • Renal Disease causes the kidneys to secrete fewer quantities of the Erythropoietin body hormone which is responsible in stimulating the development processes of Red Blood Cells. Consequently, the reduced production of the Erythropoietin hormone reduces the Red Blood Cells production leading to Low Hematocrit Levels.
  • Rheumatoid Vascular Diseases including Rheumatoid Arthritis and Lupus are associated with reduced production of Red Blood Cells leading to low Red Blood Cells count and Low Hematocrit Levels.
  • Cancers that cause elevated production of other types of blood cells (White Blood Cells for example) also reduce the production of Red Blood Cells and cause Low Hematocrit Levels. All blood cells are produced from the same stem cells and those cancers use a massive amount of the blood producing stem cells to produce blood cells other than the Red Blood Cells leading to low Red Blood Cells Count and Low Hematocrit Levels. These cancers involve:

–         Lymphoma a cancer which occurs as a result of raised production of B or T Lymphocyte White Blood Cells.

–         Hodgkin’s Lymphoma is a cancer that occurs due to increased production of the Lymphocyte White Blood Cells.

–         Leukemia is a cancer that occurs because of increased production of immature white blood cells.

–         Multiple Myeloma is a cancer which occurs due to increased production of Myeloma cells. Myeloma Cells are malignant plasma cells that accumulate in the bone marrow and reduce the production of all kinds of blood cells including the Red Blood Cells.