What Is Microcytic Anaemia?

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Microcytic anaemia is a condition where someone has smaller than normal red blood cells (RBCs) in their bloodstream, leading to fatigue and shortness of breath.1 Anaemia refers to a variety of conditions with either reduced haemoglobin concentration or reduced RBC numbers, and microcytic refers to the fact that the RBCs present are a smaller size. 

There are several causes of microcytic anaemia, and it can affect people of all ages and backgrounds. Understanding the symptoms and how they affect the body can allow for early diagnosis and, therefore, treatment.  


Firstly, it is important to understand the role of red blood cells. RBCs are very important in oxygen transport around the body. They contain a protein called haemoglobin, which acts as a carrier for oxygen. When we breathe in, oxygen from their air enters our lungs, and the haemoglobin in the RBCs binds to them. In this form, oxygen can be moved around our body in a stable form. When they reach areas with low oxygen levels, like our muscles and organs, the haemoglobin unbinds with the oxygen so that our body can use it.  

Another important characteristic of haemoglobin is that it contains iron. Therefore, any condition in which we have low iron affects how our haemoglobin and RBCs function. 

Anaemia can be caused by three main issues: 

Clinical presentation 

Symptoms of Microcytic Anaemia 

  • Tiredness 
  • Lack of energy 
  • Dizziness 
  • Shortness of breath, especially after exerting yourself 
  • Palpitations (feelings of your heart pounding or racing)
  • Pale skin

Diagnosing microcytic anaemia 

The first test that your GP will order is a blood test to look at the full blood count (FBC). This shows how many red blood cells you have, how big they are, and the concentration of haemoglobin, which will allow them to determine whether you have microcytic anaemia.

The threshold at which low haemoglobin (Hb) is classified as anaemia varies by gender and age: 

  • Children 12-14 years old: Hb<120 g/L 
  • Non-pregnant people assigned female at birth (AFAB) over 15 years old: Hb<120 g/L 
  • Pregnant people: Hb<110 g/L 
  • People assigned male at birth (AMAB) over 15 years old: Hb<130 g/L 

Once microcytic anaemia has been diagnosed, another blood test can be added to find the exact cause of this. One particular test is called iron studies, which look at how much iron is stored in your body (ferritin), how well your body absorbs iron (transferrin) and how well it is transported around the body (total iron binding capacity).

If the microcytic anaemia is suspected to be caused by difficulty absorbing iron, there are further blood tests to rule out coeliac disease (a condition of gluten sensitivity, causing lower absorption of nutrients in the small intestine). 

If these tests are not entirely conclusive of the cause, then further specialist tests can be done, in particular, a blood film. This looks at the blood under a microscope to see the shape and size of the cells. 

Causes of microcytic anaemia 

Iron deficiency anaemia 

Iron deficiency anaemia (IDA) is one of the most common types of anaemia, as a lack of iron leads to a reduction in oxygen-carrying capacity. There are several causes for IDA. In those with a uterus, heavy periods can cause a loss of blood and, therefore, RBCs. In pregnancy, there is an increased demand for iron for the baby, which can lead to IDA in the pregnant individual. 

A lack of iron in the diet can make you more likely to develop anaemia, which is why including iron-rich sources (such as meat or leafy greens) as part of a balanced diet is so essential. 

A more serious cause can be gastrointestinal blood loss. This could be due to regular use of strong drugs such as NSAIDs (e.g. ibuprofen or aspirin), stomach ulcers or any cancer throughout the gastrointestinal tract, such as stomach cancer or bowel cancer. Symptoms include sharp, sudden, severe abdominal pain, blood in stools, thick tarry stools or vomiting blood. It is vital that if you experience any of these symptoms, you should seek urgent medical advice.  


Thalassemia is an umbrella term for a group of inherited blood conditions where faulty genes cause the body to produce less haemoglobin than normal. There are different types of thalassemia, and it is also possible to have the thalassemia trait (a carrier). Depending on the form of thalassemia, the symptoms of anaemia can vary in intensity. Thalassemia is more common in people of Mediterranean, Asian or Middle Eastern descent. As an inherited condition, it can be screened for during pregnancy, and these tests are routinely offered to all pregnant individuals in England in the form of a blood test.  

 Anaemia of chronic disease 

Anaemia of chronic disease is a type of anaemia that affects people who have inflammatory conditions, such as autoimmune diseases (including rheumatoid arthritis or lupus), chronic kidney disease or cancer

Chronic inflammation can prevent the body from using its stores of iron, resulting in anaemia.  

Sideroblastic anaemia 

Sideroblastic anaemia is a rare blood disorder that affects RBC formation. In these cases, the body has enough iron, but it is not used correctly to form RBCs. Instead, cells called sideroblasts are produced, and the iron builds up around the body. 

Some forms are inherited and present in young children, but some people develop it through exposure (acquired), in particular from drinking excessive alcohol or exposure to lead or certain drugs. In some cases, there is no known reason (idiopathic). 

Symptoms of sideroblastic anaemia are similar to those of all anaemias. However, the build-up of iron around the body can also cause more serious issues, such as an enlarged liver or spleen.2   

Microcytic anaemia vs other types of anaemia 

When suspecting microcytic anaemia, the first step is to differentiate it from other types of anaemia. 

Anaemia itself is a general term for low RBCs and, therefore, low haemoglobin. However, it is subdivided into 3 types based on their size: 

This categorisation is important, as different disease processes cause the red blood cells to develop in different ways. This is reflected in the size that they become. 

Treatment and management 

Addressing underlying causes 

As mentioned before, several underlying problems can lead to microcytic anaemia. For anaemia of chronic disease, proper management of the inflammation can avoid complications. If the anaemia is caused by a loss of blood, such as through heavy periods or from a gastrointestinal source, further investigations into the reason for this are important.   

Iron supplementations and therapies 

Oral iron supplements can be given to build up more healthy red blood cells over time. This replenishes the stores of iron and also increases circulating iron for the body to use. In more serious cases, iron therapy can be given intravenously (through a vein). 

To promote absorption, vitamin C should be taken alongside iron supplements. 

Blood transfusions

In severe cases where your haemoglobin is very low or where your symptoms are severe, a bag of blood from a donor can be transfused to quickly boost your red blood cells and help you feel better faster. However, there are some risks involved, so it is only used when necessary.  

For people with severe types of thalassaemia, blood transfusions may be required regularly.3

Prognosis and complications

Untreated microcytic anaemia may lead to some serious long-term problems. If left unaddressed, the persistent lack of oxygen-carrying red blood cells can lead to chronic fatigue and weakness, significantly impacting your daily life. The lack of oxygen causes the heart to compensate by working harder, putting more strain on it to deliver fewer, smaller RBCs across the body.4

However, in general, the outlook for microcytic anaemia is positive, and there are several treatment options available to manage the symptoms. Most cases are mild and can be treated through tablets or dietary changes. However, genetic causes of microcytic anaemia, such as thalassemia may need more specialist input and might be more difficult to manage. 

With timely diagnosis and effective treatment, most of the symptoms of microcytic anaemia can be alleviated, and the body's oxygen-carrying capacity can be improved. Regular follow-up and monitoring are essential to ensure that the treatment is working well.   


As mentioned, one of the most common forms of microcytic anaemia is iron deficiency anaemia. The best way to prevent this or to alleviate the symptoms is by getting enough iron in your diet. 

Iron-rich foods include: 

  • Red meat 
  • Leafy greens 
  • Fortified cereals 
  • Beans 

One way of increasing the absorption of iron is to incorporate more vitamin C in your diet. Vitamin C works alongside iron, so it is best to try including both in your diet where possible. 

Vitamin C-rich foods include: 

  • Citrus foods  
  • Peppers 
  • Cruciferous vegetables (e.g. kale, broccoli) 

Early detection and screening play an important role in preventing microcytic anaemia. If you are having symptoms of anaemia (particularly excessive tiredness), then it may be very beneficial to be checked out by a doctor and to get a set of blood tests to investigate this.  

Thalassemia can be identified through newborn screening programmes. By identifying this in newborns, it allows for early management and reduction in potential complications.  


In conclusion, microcytic anaemia is a condition where the size of your red blood cells becomes smaller than normal. This leads to symptoms such as fatigue, weakness, and palpitations.

Causes include iron deficiency anaemia, thalassemia, anaemia of chronic disease, and sideroblastic anaemia

Getting a timely diagnosis and proper management can make a world of difference. If you notice any of these symptoms – feeling exhausted, having trouble catching your breath, or pale skin – it's essential to reach out to your doctor. Your doctor will be able to investigate this further, particularly a full blood count, to see whether you have microcytic anaemia.  

Treatment might include taking iron supplements, making some adjustments to your diet, or addressing any underlying health issues.


  1. Massey AC. Microcytic anaemia. Differential diagnosis and management of iron deficiency anaemia. Med Clin North Am. 1992 May;76(3):549–66.
  2. Rodriguez-Sevilla JJ, Calvo X, Arenillas L. Causes and pathophysiology of acquired sideroblastic anaemia. Genes [Internet]. 2022 Aug 30 [cited 2023 Aug 5];13(9):1562. Available from: https://www.mdpi.com/2073-4425/13/9/1562  
  3. Nixon CP, Sweeney JD. Severe iron deficiency anaemia: red blood cell transfusion or intravenous iron?: EDITORIAL. Transfusion [Internet]. 2018 Aug [cited 2023 Aug 6];58(8):1824–6. Available from: https://onlinelibrary.wiley.com/doi/10.1111/trf.14819  
  4. Hegde N, Rich MW, Gayomali C. The cardiomyopathy of iron deficiency. Tex Heart Inst J [Internet]. 2006 [cited 2023 Aug 5];33(3):340–4. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1592266/

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Chavini Ranasinghe

Bachelor of Medicine, Bachelors of Surgery - MBBS, University College London

Bachelor of Science in Global Health - BSc (Hons), University College London

Chavini is a junior doctor currently working within the NHS. She also has several years of experience within medical education and has published multiple scientific papers on a wide range of topics. Her exposure to clinical practice and academia has helped her to develop an interest in sharing accessible and accurate medical information to the public.

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