Hematocrit (HCT) Blood Test

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HEMATOCRIT DEFINITION Hematocrit (HCT) is the proportion, by volume (expressed in percentage), of the blood that consists of red blood cells. For example, a hematocrit of 35% means that there are 35 milliliters of red blood cells in 100 milliliters of blood. Blood is a specialized body fluid with a diversity of functions including transporting… Read More

Hematocrit (HCT) Blood Test


Hematocrit (HCT) is the proportion, by volume (expressed in percentage), of the blood that consists of red blood cells. For example, a hematocrit of 35% means that there are 35 milliliters of red blood cells in 100 milliliters of blood.

Blood is a specialized body fluid with a diversity of functions including transporting oxygen and nutrients to different organs and tissues of the body. It has four main components:

  • Red blood cells (RBCs).
  • White blood cells (WBCs).
  • Platelets.
  • Plasma.

Red blood cells are vital to your health. They bind the oxygen in your body system and transport it to various locations in your body, via your bloodstream. For you to stay healthy, your body must have the correct proportion of red blood cells. This is because a low or high proportion of RBCs in your body will result in an abnormal health condition.

An HCT blood test is used to determine if hematocrit levels are of the low, high, or normal range.

A hematocrit can help your doctor diagnose a particular health condition in your body, or it can determine how well your body is responding to a particular treatment. Apart from various other reasons, doctors most often use hematocrit tests for:

  • Anemia (lack of blood).
  • Leukemia (cancer of the blood).
  • Dehydration.
  • Dietary deficiency.

Alternatively, your doctor can order a complete blood count (CBC) test. CBCs include hematocrit test, as well as:

  • Hemoglobin test.
  • Reticulocyte count.

Looking at your overall blood test results, the doctor will have an understanding of your red blood cell count. CBC is a common test that screens your blood for certain disorders that can affect your health. It also determines if there are any increases or decreases in your blood cell count. 

Normal values vary, based on your age and gender. Your lab report will reveal the normal value range for your age and gender. With CBC, we can diagnose a broad range of conditions, ranging from anemia and other infections to cancer. Typical hematocrit levels are as follows:

  • Adult men 38.8% to 50.2%
  • Adult women 34.9% to 44.5%

Children aged 15 and under have a separate set of ranges since their hematocrit levels change rapidly with time. The hematocrit range for a child of a certain age will be determined by the specific lab responsible for the analysis of the results.


Blood Sample:

  • A small sample of your blood will be needed for your hematocrit test.
  • The blood will be taken from a vein in your arm, or drawn from a pin piercing on your finger.

If the hematocrit test is to be obtained a complete blood count (CBC):

  • A lab technician will draw blood from your vein, either from the inside of your elbow or the back of your hand.
  • A portion of your skin where the blood is to be drawn will be cleaned with an antiseptic.
  • An elastic band or tourniquet will be tied around your upper arm to help the vein swell with blood.
  • The technician will insert a needle in the vein and collect a blood sample in one or more vials.
  • He will remove the elastic band and cover the punctured area with a bandage, to stop the bleeding.
  • You may experience minor bruising, which will clear up within a few days.
  • Your sample is then sent to a lab for analysis.


Your HCT range is evaluated using a centrifuge (a machine that spins at a high frequency).

  • An anticoagulant is added to the blood sample, to keep your blood from clotting.
  • The blood sample in a test tube is pinned in at a high rate in a centrifuge (which causes the contents of your blood to separate).
  • The test tube is brought out of the centrifuge and the sample will separate into 3 parts (red blood cells, plasma (the fluid in your blood), and anticoagulants).  The RBCs will occupy the lower bottom of the tube.
  • The red blood cells (RBCs) are then compared to a guide that reveals what proportions of your blood they make up.

Hematocrit Normal Range:

Some laboratories have their special ranges for hematocrit. The generally accepted ranges (a standard) for hematocrit depend on your gender and age. Normal hematocrit levels are determined by ages and are as follows:

Age Hematocrit Range
Adult males 42% to 54%
Adult women 38% to 46%
Newborns 55% to 68%
One week old 47% to 65%
One month old 37% to 49%
Three months old 30% to 36%
One year old 29% to 41%
Ten years old 36% to 40%


These values may vary slightly among different laboratories.

Low Hematocrit Result:

Low hematocrit indicates the anemic condition. There are many causes of anemia. Some common reasons are:

  • Loss of blood (via traumatic injury, bleeding, surgery, and colon cancer).
  • Bone marrow problems (eg: replacement of bone marrow by cancer).
  • Suppression by chemotherapy drugs.
  • Abnormal hemoglobin (sickle cell anemia).
  • Nutritional deficiency in nutrients such as iron, folate, vitamin B12, etc.

High Hematocrit Result:

High hematocrit indicates abnormally elevated red blood cell (RBC) counts. This is typical of:

  • People living at high altitudes, such as hills or mountains.
  • Chronic smokers, such as chain-smokers.

Abnormally elevated RBC levels are also proofs of abnormal health conditions like:

  • Dehydration (which can be restored when the body is normally hydrated).
  • Lung disease.
  • Certain tumors.
  • Bone marrow disorder (medically known as polycythemia Rubia vera).
  • Erythropoietin (Epogen) drug abuse; common among athletes.


These include:

  • Fatigue or tiredness.
  • Shortened breath.
  • Increased heart rate.
  • Dizziness or sleepiness.
  • General weakness.


  • Fatigue.
  • Joint pain.
  • Shortened breath.
  • Itchy skin, especially after a shower.
  • Disturbance of sleep (also known as insomnia).
  • Tenderness in the palms of the hands or soles of the feet.


A hematocrit test is not associated with any major risks. Patients return to their normal working life, after the procedure. 

You may have pricking, some bleeding, and/or throbbing at the site where the blood is drawn. Bleeding and swelling at the puncture site will stop within a few minutes after the test. 

If you experience persistent swelling or bleeding that doesn’t stop within some minutes of pressure being applied to the puncture site, feel free to report to the doctor, with immediate effect.


Several factors can an accurate outcome of a hematocrit test. These are as follows:

  • Smoking.
  • Pregnancy.
  • Severe dehydration.
  • Recent blood transfusion.
  • The significant recent loss of blood.
  • Living at high altitudes, such as mountains, plateau, or hills.


  • What do hematocrit levels indicate?

A hematocrit test measures how much of your blood is made up of red blood cells (RBCs). These RBCs contain a protein called hemoglobin which is responsible for carrying oxygen from your lungs to the rest of your body. Too high or too low hematocrit levels can indicate a blood disorder, dehydration, or other medical conditions.

  • What is a good hematocrit level?

The normal levels of hematocrit for adult women range from 38% to 46%, while that of men is from 42% to 54%. These values may however be slightly varied among different labs.

  • Why is hematocrit important?

Hematocrit is a simple blood test done to measure the percentage of red blood cells in a person’s blood. Erythrocytes (red blood cells) are important because they carry oxygen through your body. A low or high red blood cell (RBC) count can indicate a medical condition.

  • Which is more important: hemoglobin or hematocrit?

The important message for nephrologists is that hemoglobin is always superior to hematocrit for monitoring anemia of renal disease because it can be measured with greater accuracy, both within and between labs. Hb (hemoglobin) and HCT (hematocrit) are both excellent correlates of anemia and correlate well with one another.

  • What causes low hematocrit in blood tests?

The causes of low hematocrit may likely be or include ulcers, traumatic bleeding, colon cancer, internal bleeding, sickle cell anemia, enlarged spleen, bone marrow suppression, cancer, drugs, and decreased production, as well as the destruction of red blood cells.