Haematocrit Blood Test

What is a Haematocrit blood test?

The haematocrit (Hct) blood test is a laboratory test that checks how much of your blood is made up of red blood cells. It is also referred to as Packed Cell Volume (PCV) as it measures the volume of packed red blood cells relative to other cells in the blood. The different parts of your blood include white blood cells, platelets, and a liquid called plasma. When blood is centrifuged or spun in a special tube, it separates into red blood cells or erythrocytes at the base, buffy coat containing white blood cells or leucocytes and platelets in the middle, and liquid plasma at the top.

Red blood cells contain the protein haemoglobin, which carries oxygen from your lungs to the entire body. The Haematocrit blood test estimates the volume or percentage of red blood cells in your blood, thus determining the status of red blood cells for their essential functions.

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Why is a Haematocrit blood test done?

A haematocrit blood test is typically performed as part of a Complete Blood Count with or without differential. Your doctor will recommend this test due to the following reasons:

• To review your overall health: As a component of a routine medical examination, to monitor your general health and to screen for different disorders such as anemia or cancer.
• To diagnose a medical condition: In case you have weakness, fatigue, fever, inflammation, bruising or bleeding.
• To monitor a medical condition: In case you have been diagnosed with iron deficiency anaemia or secondary polycythemia.
• To monitor medical treatment: In case you are taking medications that may affect red blood cell and haematocrit levels in blood.

What conditions cause a change in the Haematocrit?

The conditions that cause a change in the red cell count will cause a change in the haematocrit.

Low haematocrit

A low hematocrit indicates anaemia. Anaemia is caused by both factors that cannot be changed and others that can be changed.  The non-modifiable factors include your family history and age, whereas modifiable factors include dietary habits and other health conditions that affect the production of red blood cells. The causes of a low red haematocrit include:

• Age: Ageing increases your possibility of developing anaemia.
• Family history: A family history of inherited types of anaemia increases your risk of having a low hematocrit.
• Dietary habits: When your diet is deficient in nutrients such as iron, vitamin B12, and folic acid, which help in making healthy red blood cells, you have a higher risk of anaemia. Drinking excessive alcohol also raises your risk of anemia.
• Blood loss: Your risk of a low red cell count and haematocrit increases if you have any condition that increases your risk of losing a lot of blood. These include excessive loss of blood during menstruation, due to inflammation in the stomach or bowels, bleeding from surgery, a serious injury, or frequent blood donations. Pregnancy is associated with a low red blood cell count due to the expansion of fluid volume; however, excessive blood loss during childbirth can also cause a low haematocrit.
• Other health conditions: Health conditions such as chronic kidney disease, inflammation from an infection, cancer, or an autoimmune disease such as rheumatoid arthritis can cause your body to produce fewer red blood cells and have a low hematocrit. Your risk of low Hct can also be raised with certain medicines or treatments, such as chemotherapy for cancer.

High haematocrit

A high haematocrit indicates polycythemia. Polycythemia can be spurious or true polycythemia.

Spurious Polycythemia: This occurs due to a decrease in blood volume rather than an increase in true red blood cell mass. The causes include:

• Severe dehydration caused by fluid loss resulting from diarrhea and severe vomiting.
• Gaisbock syndrome, which commonly occurs in obese men with high blood pressure. Smoking, excessive alcohol, and the use of diuretics (medications that promote urination) are risk factors. 

True Polycythemia: True polycythemia can be primary or secondary based on serum erythropoietin (EPO) levels. Erythropoietin is a hormone that supports the production of RBCs.

Primary polycythemia (low serum EPO): Occurs due to disorders of the bone marrow:

• Polycythemia vera
• Primary familial and congenital polycythemia

Secondary polycythemia (high serum EPO): Occurs in other conditions:

• High altitude
• Lung conditions: Chronic obstructive pulmonary disease (COPD), uncontrolled asthma, sleep apnea
• Congenital heart conditions
• Kidney conditions: Renal cysts, kidney cancer, stenosis of the renal artery
• Increased carboxyhemoglobin: Generally seen in smokers, people working on cars in closed spaces, or people working in boiler rooms
• Disorders of haemoglobin: High-affinity haemoglobins such as Hb Yakima, methemoglobinemia
• Erythropoietin-secreting tumors in the liver, uterus, and brain
• Medications: Anabolic steroids, testosterone replacement therapy, and erythropoietin analog

What are the symptoms of low and high Haematocrit?

Low haematocrit

 Your body does not receive enough oxygen-rich blood when you have low red blood cells. The lack of oxygen can cause fatigue, pale skin, shortness of breath, dizziness, headaches, an irregular heartbeat or cold hands and feet.

Low hematocrit can cause an irregular heartbeat and heart failure, worsen infections and other health conditions, and lead to pregnancy complications.

High haematocrit

A high haematocrit causes your blood to thicken and become sluggish due to an increased red cell mass. Thick blood doesn’t flow as quickly, depriving your organs of oxygen. Symptoms of a high haematocrit include headaches, fatigue, blurred or double vision, dizziness, and blood clots. You may experience itching after taking a warm shower.

Prolonged history of smoking, staying at high altitudes, congenital heart disease, and family history of haemoglobin disorders are risk factors for polycythemia.

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How do you prepare for your Haematocrit blood test?

No special preparations are required for a haematocrit blood test.

A haematocrit blood test is ordered as part of a complete blood count (CBC). You are not required to fast for this test; however, you may be required to fast for 8-12 hours, depending on other tests you may have scheduled. It is recommended to stay hydrated by consuming an adequate amount of water when fasting. Your doctor will let you know if you need to follow any special instructions.

How is a Haematocrit blood test done?

The general steps of a blood test involve the following:

• A medical laboratory technician will check your arms for a vein that can be reached comfortably. This is usually in the inner part of your arm on the other side of your elbow
• Upon location of the vein, they would clean and disinfect the area
• They would then insert a small needle into your vein to draw a blood sample, which might feel like a slight pinch
• After they insert the needle, a small amount of blood will collect in a test tube
•  They will remove the needle and press the bleeding site with a cotton ball or gauze to stop the bleeding
• A bandage will be applied on the site and the collection of the sample will be done
• After a healthcare provider has collected your blood sample, they’ll send it to a laboratory for testing. Once the test results are back, your doctor will share the results with you

Interpretation of test results

The normal reference range of a haematocrit blood test for adults is 0.4-0.5L/L. 

Values lower than 0.4L/L are termed anaemia or low haematocrit. Values higher than 0.5L/L are called polycythemia or high haematocrit. Several factors can influence the levels of red blood cells and haematocrit in your body. Your doctor may repeat the test or recommend additional testing based on your signs and symptoms.

What can you do in case of low or high Haematocrit?

Low Haematocrit

Improve nutrient status

Inadequate dietary iron intake and deficiencies in folate, vitamin B12, vitamin A, and riboflavin can result in anaemia as they play essential roles in the production of red blood cells. 

Your doctor will recommend taking oral supplementation of iron and vitamin B12 if your dietary intake is inadequate. You should increase your dietary intake of iron, vitamin B12 and other vitamins. Some sources of iron include green leafy vegetables, lentils, fortified grains, chicken, lean cuts of beef, liver. Sources of vitamin B12 include meat, fish, poultry, plant-based milks such as soy and almond milk, and fortified cereals. 

Reduce infection, inflammation, and chronic diseases

Infections such as malaria, tuberculosis, HIV,  parasitic infections decrease nutrient absorption and metabolism or can cause nutrient loss. In addition, some chronic conditions such as kidney disease, cancer, diabetes, obesity cause inflammation that can lead to anaemia, known as anaemia of inflammation or anaemia of chronic disease.

Identifying the exposure and early signs of infection can help you and your doctor manage the disease from the onset. This will prevent their progression and affect the red blood cell levels and haematocrit. Additionally, regular blood screening tests are necessary to monitor for chronic conditions. 

Reduce women’s health conditions 

Regular menstrual losses, natural increase in maternal blood volume during pregnancy, and blood loss during and after childbirth commonly lead to anaemia.

Women in childbearing age and during pregnancy should have regular check-ups and monitoring of their red blood cell count with various blood tests. 

Improve screening and management of inherited red blood cell disorders

Inherited red blood cell disorders affect haematocrit and haemoglobin production, either the quantity, such as thalassemia, or the quality, such as sickle cell disorders. These conditions are quite common among populations living in Africa, Asia, and the Western Pacific, as well as among people with ancestry from these regions. 

Screening for these disorders in populations is essential, as it would affect how other interventions, such as iron supplementation, are managed. You may require appropriate genetic counseling to obtain information about the inherited aspects of these conditions and the risk of passing on the diseases.

High haematocrit

There is no definitive cure for a high haematocrit, which causes polycythemia. Management goals are aimed at symptom relief and reducing the risk of disease complications, including clot formation and, bleeding. Your doctor can recommend treatment options such as phlebotomy or blood letting.  Low-dose aspirin is also an option for blood thinning. However, you should set your goal to regulate your heart health, including optimising your weight, engaging in regular exercise, planning for smoking cessation, and maintaining a healthy blood pressure.

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Sources:

1. Mondal H, Zubair M. Hematocrit. [Updated 2024 Oct 6]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK542276/

2. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Anemia; [updated 2022 March 24]. https://www.nhlbi.nih.gov/health/anemiaclerk

3. Pillai AA, Fazal S, Mukkamalla SKR, et al. Polycythemia. [Updated 2023 May 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526081/

4. World Health Organization - Accelerating anaemia reduction: a comprehensive framework for action.

https://iris.who.int/bitstream/handle/10665/367661/9789240074033-eng.pdf?sequence=1.