Haemoglobin Blood Test

What is Haemoglobin?

Haemoglobin is a vital protein found in your red blood cells. Haemoglobin is made up of proteins called heme and globin. The heme part contains iron, which permits it to bind to oxygen. Your red blood cells carry oxygen from your lungs to other tissues and organs throughout your body with the help of haemoglobin.

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What factors affect Haemoglobin levels?

Many factors affect the level of haemoglobin in your body. Your red blood cells are produced in your bone marrow, and factors affecting their production affect the level of haemoglobin in your body. These include:

• Inadequate production of red blood cells by your bone marrow: Conditions and diseases can cause this that affect your bone marrow’s ability to produce or support enough red blood cells.
• Increased destruction of cells: Your body produces enough red blood cells, but the cells are getting destroyed quicker than your body can replace them.
• Loss of blood from injury or illness: Iron and haemoglobin are lost anytime you lose blood. For instance, menstruating women and internal bleeding due to a bleeding ulcer both affect the haemoglobin levels
• Inadequate absorption of iron in your body: This affects your body’s ability to develop red blood cells.‍
• Deficiency of essential nutrients: Minerals such as iron, vitamins B12 and B9 are essential for haemoglobin production. Their inadequate supply and absorption slow down the production of haemoglobin.

When is a Haemoglobin blood test done?

Your doctor might recommend a haemoglobin test under the following conditions:  

Routine blood test

Haemoglobin tests are done as part of a complete blood count (CBC) test. This test measures the number of red blood cells, white blood cells and platelets in a blood sample, allowing your provider to assess your health and screen for certain conditions.

Monitoring existing conditions

If you are diagnosed with anaemia or blood-related conditions, then a haemoglobin test is an essential measure to monitor your response to treatment.

Symptoms of low or high haemoglobin levels

If you experience symptoms indicating low or high haemoglobin levels, then a haemoglobin test is vital to perform.

With low haemoglobin or too few red blood cells, your tissues and organs do not receive the oxygen required to make energy and keep you healthy. Symptoms of low haemoglobin include fatigue, pale skin, weakness, dizziness, shortness of breath, cold hands and feet. On the other hand, high haemoglobin or too many red blood cells can cause your blood to thicken and become sluggish. Thick blood doesn’t flow as quickly, depriving your organs of oxygen. Symptoms of high haemoglobin include headaches, blurred or double vision, dizziness, itching, and blood clots.

Why is a Haemoglobin blood test done?

A haemoglobin blood test is done to estimate the amount of haemoglobin in your red blood cells. Haemoglobin is an indispensable protein in your body as it carries oxygen. Hence, measuring haemoglobin estimates the oxygen-carrying capacity of your blood. This is useful for people of all age groups and helps improve the quality of life. 

Haemoglobin blood test provides valuable information about your body, both in health and disease. It provides a general screening of your health and determines whether you have low (anaemia) or high (polycythaemia) haemoglobin levels. This helps in the early detection of conditions that cause changes in haemoglobin levels, allowing for timely management. Further, if you are diagnosed with a health condition or have symptoms of low anaemia, the initiation and monitoring of treatment can be done. In addition, a haemoglobin blood test measures your ability to handle blood loss and the need for a blood transfusion before and after surgery.

What conditions cause a change in Haemoglobin levels?

Numerous conditions can cause a change in the haemoglobin levels, shifting them to low or high levels.

Low Haemoglobin levels

The conditions with low haemoglobin are characterised by anaemia. The mechanisms for the onset of anaemia involve a reduction in the number of red blood cells, which can occur due to blood loss, increased destruction of red blood cells or inadequate production of cells. 

Blood loss can occur due to acute or chronic causes

• Acute: Surgery, trauma, excess menstrual bleeding
• Chronic: Blood losses from the gut due to hookworm infestation, ulcers; urinary losses due to kidney cancer, enlargement of the prostate

Increased destruction of red blood cells causes haemolytic anaemia

• Acquired:  Mediated by the immune system, infection, blood transfusion-related, and increased size of the spleen
• Hereditary: Disorders of haemoglobin such as sickle cell anaemia, defects in red blood cell metabolism such as G6PD deficiency, and defects in red blood cell membrane production such as hereditary spherocytosis

Defective production of red blood cells

Defective production of red blood cells results in the production of different sizes of red blood cells. Based on the size of red blood cells, anaemia is classified as microcytic (small-sized red blood cells), normocytic (normal-sized red blood cells), and macrocytic (large-sized red blood cells) anaemia.

Iron-deficiency anaemia results in red blood cells that are small in size. It is typically seen in women of childbearing age as an outcome of poor dietary intake of iron and the monthly loss of blood associated with menstrual cycles. Similarly, poor nutrition, especially of iron and folic acid. leads to anaemia in elderly patients. Vegetarian population, and alcoholics are at risk groups for B12 and folic acid deficiency, causing red blood cells to be of a larger size.

High Haemoglobin levels

If your haemoglobin levels are high, you are likely to develop polycythaemia vera. Polycythaemia vera consists of unregulated red blood cell production that leads to an increased red blood cell mass. There is also an increase in the production of white blood cells and platelets.

Primary polycythaemia occurs due to a defect in the bone marrow. On the other hand, secondary polycythaemia occurs due to various causes such as conditions causing deprivation of oxygen or hypoxia, such as high altitude, smoking, tumours secreting erythropoietin, or hormones stimulating the production of red blood cells.

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How do you prepare for your Haemoglobin blood test?

No special preparations are required for a haemoglobin blood test.

A haemoglobin 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 Haemoglobin 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 to 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

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Normal haemoglobin levels vary for females and males. The optimal reference range of haemoglobin for females is 120-160g/L and for males is 140-180 g/L. The values lower than 120g/L in females and 140g/L in males are termed as anaemia, while values greater than 160g/L in females and 180g/L in males are categorised under polycythemia. While these are descriptive terms, many other factors play a role in classifying the low and high haemoglobin values. Your doctor will recommend additional testing based on your signs and symptoms.

What can you do in case of low or high Haemoglobin levels?

Low Haemoglobin levels

Improve nutrient status

Iron deficiency is the most common nutritional deficiency leading to anaemia. Inadequate dietary iron intake and deficiencies in folate, vitamin B12, vitamin A, and riboflavin can also result in anaemia as they play important roles in the production of haemoglobin and 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, and 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 are another significant cause of anaemia. These are directly related to the areas where they are prevalent, such as malaria, tuberculosis, HIV, and parasitic infections. Infections can decrease nutrient absorption and metabolism or can cause nutrient loss. In addition, some chronic conditions, such as kidney disease, cancer, diabetes, and 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 haemoglobin levels. In addition, regular blood screening tests are required 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 and increased mortality.

Women of childbearing age and during pregnancy should have regular check-ups and monitoring of their haemoglobin with various blood tests. This would facilitate the early detection and management of anaemia.

Improve screening and management of inherited red blood cell disorders 

Inherited red blood cell disorders are significant causes of anaemia, particularly in areas where malaria is or has been endemic. Some of these conditions affect haemoglobin production, either the quantity, such as thalassemia, or 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. This may cause low haemoglobin levels.

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

High haemoglobin levels

There is no definite cure for high haemoglobin levels causing polycythemia vera. 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 phlebectomy or blood clotting. Low-dose aspirin is also an option for blood thinning. However, you should set your goal to regulate your cardiovascular health, including optimising weight, engaging in exercise, planning for smoking cessation, and maintaining your blood pressure.

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Sources

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

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

2. Turner J, Parsi M, Badireddy M. Anemia. [Updated 2023 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499994/.

3. Lu X, Chang R. Polycythemia Vera. [Updated 2023 Apr 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK557660/.

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