Erythrocytes, commonly known as red blood cells (RBCs), play a vital role in the human body by facilitating the transportation of oxygen and nutrients to various organs and tissues. Their distinctive characteristics in terms of structure and composition enable them to carry out these essential functions efficiently. The significance of erythrocytes is important in the exploration of different diseases across multiple body systems.
One diagnostic test that provides valuable insights into the role of erythrocytes is the hematocrit test. A hematocrit test or HCT blood test determines the percentage of red blood cells in your blood. Along with red blood cells, blood also consists of white blood cells, platelets, and plasma. Abnormal hematocrit levels, whether too high or too low, can indicate the presence of blood disorders, dehydration, or other medical conditions that impacts your blood.
The hematocrit blood test is also known by various names, such as packed cell volume (PCV), HCT blood test, and H and H (referring to hematocrit and haemoglobin).
Why is it done?
A Hematocrit test is frequently included in a complete blood count (CBC), which is a routine blood test that assesses the different components of your blood. This test is used to evaluate your overall health and can also aid in the diagnosis of various blood disorders.
These disorders include:
- Anaemia – Anaemia occurs when the production of healthy red blood cells in your blood is lower than normal. This deficiency of red blood cells leads to a reduced supply of oxygenated blood to your body. Insufficient oxygen can result in feelings of fatigue and weakness.
- Polycythaemia – Polycythaemia is a condition characterised by an excessive presence of red blood cells in the body. This surplus of cells thickens the blood, which raises the likelihood of various health complications, including the formation of blood clots.(1,3)
- Leukaemia – In cases of leukaemia, the presence of leukaemia cells in the bone marrow can lead to a reduction in the number of healthy red blood cells. The leukaemia cells essentially take up space in the bone marrow, displacing the production of normal red blood cells. As a result, individuals with leukaemia may have a lower-than-normal count of red blood cells.
- Dehydration
- Dietary deficiencies
A hematocrit blood test may be included in your routine check-up or prescribed by your healthcare provider to monitor your health during cancer treatment or for ongoing health conditions. This test can also be ordered if you are experiencing symptoms associated with red blood cell disorders like polycythaemia or anaemia.
Symptoms of polycythaemia
- Headache
- Fatigue or general weakness
- Difficulty breathing or shortness of breath
- Sensation of light-headedness or dizziness
- Vision problems such as blurred or double vision, as well as blind spots
- Profuse sweating, particularly during sleep
- Gum bleeding and excessive bleeding from minor cuts
- Skin-related issues like itching following a shower or bath, a burning sensation, or facial redness
Symptoms of anaemia
- Fatigue or feelings of weakness
- Difficulty breathing or experiencing shortness of breath
- Dizziness
- Irregular heartbeat or arrhythmia
- Headache
Normal range for hematocrit levels
The normal range for hematocrit levels varies depending on age and gender.
- Adult males typically have hematocrit levels ranging from 41% to 50%
- Adult females generally have hematocrit levels ranging from 36% to 44%
- Infants typically have hematocrit levels ranging from 32% to 42%
- New-borns typically have higher hematocrit levels, ranging from 45% to 61%.
High Hematocrit Value
An elevated hematocrit level can indicate various conditions, including polycythaemia vera. It is essential to consult your healthcare provider for accurate information regarding your test results. Several conditions can contribute to high hematocrit levels. These include:
- Dehydration: Dehydration reduces the overall water content in the body, including reduced plasma levels in the blood, resulting in an increase in the ratio of red blood cells to blood volume, leading to elevated hematocrit levels.
- Heart disease: Research indicates that high hematocrit levels can raise the risk of developing cardiovascular disease.
- Lung scarring or thickening: Scarring in the lungs can impede the effective transport of oxygen by red blood cells throughout the body.
- Smoking: Smoking impacts hematocrit levels in two ways. It stimulates the production of erythropoietin, a kidney hormone responsible for red blood cell production, resulting in an increased red blood cell count and elevated hematocrit levels.
- Obstructive sleep apnea: Studies have identified a connection between obstructive sleep apnoea and higher hematocrit levels.
- Carbon monoxide poisoning: Carbon monoxide affects the capillaries, reducing plasma volume in the blood and leading to an increase in red blood cell count, consequently elevating hematocrit levels.
- Testosterone use: Research suggests that the use of testosterone can raise the number of red blood cells, resulting in higher hematocrit levels.
Low Hematocrit Value
The primary reason for conducting hematocrit testing is to investigate suspected cases of anaemia, which is the most prevalent condition associated with this test. It is crucial to consult your healthcare provider for accurate information regarding your test results.
Additionally, other conditions that may prompt hematocrit testing include:
- Leukaemia: In leukaemia, abnormal cells in the bone marrow displace healthy red blood cells, resulting in a decreased number of red blood cells.
- Blood loss due to injury or illness: Loss of blood affects the number of red blood cells, leading to lower hematocrit levels.
- Hemolytic anaemia: This condition occurs when red blood cells break down or die at a faster rate than the body can replenish them.
- Thyroid disease: Thyroid hormones play a role in supporting red blood cell production. Insufficient red blood cells lead to decreased hematocrit levels.
- Kidney disease: Reduced hematocrit levels can indicate anaemia, a common complication of kidney disease.
- Hyponatremia: Excess water in the body can dilute the blood, resulting in lowered hematocrit levels.
Preparations required for the HCT blood test
There are no specific requirements for preparation before a Hematocrit test. However, if your healthcare provider has requested additional tests on the same blood sample, you might be advised to fast (abstain from eating or drinking) for a few hours before the test. Your provider will inform you of any specific instructions to follow.
What to expect during the HCT blood test?
The first step involves undergoing a blood test, during which a sample will be taken from you. Following that, the blood sample will be sent to a laboratory for assessment.
Blood collection
To test your hematocrit, a healthcare professional will need a small blood sample. This sample can be obtained through a finger prick or by drawing blood from a vein in your arm.
When the hematocrit blood test is included in a CBC, a lab technician will collect a blood sample by carefully drawing it from a vein. The usual locations for vein selection are the inner elbow or the back of the hand. Before the procedure, the technician will sanitise the skin using an antiseptic solution. Additionally, they will apply an elastic band or tourniquet around the upper arm to facilitate vein to swell and promote blood flow.
Subsequently, a needle will be inserted into the chosen vein to collect a blood sample, typically in one or multiple vials. The elastic band will be removed, and a bandage will be applied to the puncture site to control bleeding. It is important to note that a blood test can cause slight discomfort, often characterised by a pinching or pricking sensation when the needle punctures the skin. Some individuals may also feel lightheaded or faint at the sight of blood. Minor bruising might occur but will typically fade within a few days. The entire procedure usually takes only a few minutes, and you can resume your regular activities afterwards. The collected sample will be sent to a laboratory for evaluation.
Evaluation
In the laboratory, your hematocrit will be assessed using a centrifuge, a high-speed machine that separates the components of your blood. To prevent clotting, a lab specialist will introduce a specific anticoagulant into your blood sample.
Once the test tube is removed from the centrifuge, it will have separated into three distinct layers:
- Anticoagulant
- Red blood cells
- Plasma, which is the fluid component of your blood
Following separation, each component will settle in different parts of the tube, with the red blood cells moving to the bottom. These red blood cells are subsequently compared to a reference guide that indicates the proportion they constitute in your blood.
Accuracy of the HCT blood test
Several factors have the potential to influence the results of a hematocrit test, leading to inaccurate or deceptive outcomes. These factors include:
• Residing at high altitudes
• Pregnancy
• Severe dehydration
• Recent substantial blood loss
• Recent blood transfusion
When interpreting the results of your hematocrit test, your healthcare provider will consider these potential complicating factors. In cases where the results provide conflicting or unexpected information, your doctor may recommend repeating the hematocrit test and conducting additional blood tests.
Risks associated with the HCT blood test
The process of having your blood drawn carries minimal risks. The size of veins and arteries can vary among individuals and even between different sides of the body. As a result, obtaining a blood sample may be more challenging for some people than others.
Although the risks associated with blood drawing are generally minor, they may include:
- Feelings of faintness or light-headedness
- Excessive bleeding
- Multiple attempts to locate suitable veins
- Infection (a slight risk whenever the skin is punctured)
- Formation of a hematoma (accumulation of blood under the skin)
