In short: Macrocytic anaemia means your red blood cells are larger than normal — most often because of low vitamin B12 or folate. A simple blood test can identify it, and the right treatment depends on the underlying cause.
What Is Macrocytic Anaemia?
Anaemia means your blood does not have enough healthy red blood cells, or enough of the oxygen-carrying protein inside them called haemoglobin. When levels are low, your body gets less oxygen, which can leave you feeling tired and run down.
Doctors describe anaemia partly by the size of the red blood cells, measured on a blood test as the mean cell volume (MCV). "Macrocytic" means the red blood cells are larger than normal — the opposite of microcytic anaemia, where the cells are too small.
Large red blood cells are often a sign that the body is having trouble making them properly. Two of the most common reasons are a lack of vitamin B12 or folate (also called vitamin B9). Both are needed for the body to build healthy red blood cells.
Why B12 and Folate Matter
Vitamin B12 and folate are essential for making the genetic material (DNA) inside every new cell, including red blood cells. When either is in short supply, the bone marrow produces red blood cells that are large, fewer in number, and do not work as well. This particular pattern is sometimes called megaloblastic anaemia.
Not all macrocytic anaemia is caused by vitamin deficiency. Other causes can include regular alcohol use, certain liver conditions, an underactive thyroid, some medicines, and bone marrow conditions. This is why proper testing matters — the treatment depends entirely on the cause.
Symptoms to Look Out For
Macrocytic anaemia often develops slowly, and symptoms can be vague at first. They may include:
- Tiredness, weakness, or low energy
- Shortness of breath
- Pale skin
- Dizziness or light-headedness
- A fast or irregular heartbeat
- A sore, smooth, or red tongue, or mouth ulcers
- Reduced appetite
Symptoms That Can Point to Low B12
Vitamin B12 deficiency can affect the nervous system, sometimes even before anaemia appears. These symptoms are important not to ignore, because if left untreated for a long time some nerve damage may not fully reverse. They can include:
- Pins and needles, tingling, or numbness in the hands and feet
- Problems with balance or walking
- Memory problems or difficulty concentrating
- Changes in mood, such as low mood or irritability
If you notice persistent tingling, numbness, or balance problems, see your GP rather than waiting.
What Causes B12 and Folate Deficiency?
Vitamin B12 Deficiency
Vitamin B12 is found almost entirely in animal foods, and the body needs a healthy stomach and bowel to absorb it. Common causes of deficiency include:
- A vegan or strict vegetarian diet without supplementation, since plant foods contain very little B12
- Pernicious anaemia — an autoimmune condition where the body cannot absorb B12 properly. It is one of the leading causes of B12 deficiency, particularly in older adults.
- Other absorption problems, such as previous stomach or bowel surgery, or conditions like coeliac disease
- Long-term use of some medicines, including metformin (for diabetes) and proton pump inhibitors (for reflux)
- Older age, as absorption can become less efficient over time
Folate Deficiency
Folate is found in many foods but is not stored in large amounts, so levels can fall within weeks if intake drops. Causes include:
- A diet low in fresh vegetables and wholegrains
- Increased need during pregnancy
- Regular heavy alcohol use
- Conditions that affect absorption, such as coeliac disease
- Some medicines, including methotrexate
Who Is Most at Risk?
You may be at higher risk of B12 or folate deficiency if you:
- Follow a vegan or strict vegetarian diet
- Are an older adult
- Have an autoimmune or digestive condition such as pernicious anaemia or coeliac disease
- Have had stomach or bowel surgery
- Drink alcohol heavily
- Take certain long-term medicines (such as metformin or reflux medicines)
- Are pregnant or planning a pregnancy
How Is It Diagnosed?
Macrocytic anaemia is identified through blood tests, which your GP can arrange:
- A full blood count (FBC) — shows low haemoglobin and a high MCV (large red blood cells)
- Vitamin B12 and folate levels — to check for deficiency
- Further tests where needed — for example, antibody tests to look for pernicious anaemia, thyroid tests, or other investigations to find the underlying cause
You can have these tests done conveniently — find out more about pathology and blood tests at our clinic.
Treatment Options
Treatment focuses on replacing the missing vitamin and addressing the underlying cause. With the right treatment, the blood count usually improves over time.
Dietary Sources
Where deficiency is mild and diet-related, eating more of these foods can help — alongside your GP's advice:
- Vitamin B12: meat, fish, eggs, milk, cheese, and other dairy foods. People following a vegan diet are advised by the Australian Dietary Guidelines to take a B12 supplement, since plant foods are not a reliable source.
- Folate: leafy green vegetables, legumes, citrus fruits, and folate-fortified breads and cereals. In Australia, folic acid is added to most wheat flour used for bread, which helps support folate intake across the community.
Supplements and Injections
The right treatment depends on the cause:
- Folate deficiency is usually treated with folic acid tablets, together with dietary changes.
- Vitamin B12 deficiency may be treated with B12 injections or high-dose tablets. When the problem is poor absorption — as in pernicious anaemia — injections are often used, and treatment may need to continue long term.
An important safety point: if you have both low B12 and low folate, B12 generally needs to be treated as well, not folate alone. Taking folate by itself when B12 is also low can mask the problem and allow nerve damage to progress. This is one of the key reasons to have deficiencies properly diagnosed and treated under medical guidance rather than self-treating.
A Note on Pregnancy
Folate is especially important before and during early pregnancy, because it helps protect the developing baby against neural tube defects such as spina bifida. In Australia, women who are planning a pregnancy or are in the early stages are generally advised to take a folic acid supplement. Your GP can give you advice tailored to your situation.
How Reliance Medical Centre Can Help
Our GPs at Reliance Medical Centre in Truganina can help you make sense of symptoms such as ongoing tiredness, arrange the appropriate blood tests, identify the cause, and develop a management plan suited to your needs. We provide:
- General practice consultations to assess your symptoms
- On-site pathology referrals for blood tests
- Ongoing review, treatment, and follow-up
To discuss your health, book an appointment online or call us on (03) 9958 6699.
Frequently Asked Questions
What causes macrocytic anaemia?
Macrocytic anaemia means the red blood cells are larger than normal. The most common causes are low vitamin B12 or low folate, both of which are needed to make healthy red blood cells. Other causes include regular alcohol use, some liver conditions, an underactive thyroid, certain medicines, and bone marrow conditions.
What are the symptoms of vitamin B12 deficiency?
Symptoms can include tiredness, pale skin, shortness of breath, a sore or smooth tongue, and mouth ulcers. Vitamin B12 deficiency can also affect the nervous system, causing pins and needles, numbness in the hands and feet, balance problems, memory difficulties or mood changes. These nerve symptoms should not be ignored, as long-standing damage may not fully reverse.
How is macrocytic anaemia diagnosed?
It is diagnosed through blood tests. A full blood count (FBC) shows low haemoglobin and a high mean cell volume (large red blood cells), and your GP will check your vitamin B12 and folate levels. Further tests, such as antibody tests for pernicious anaemia or thyroid tests, may be done to find the cause.
Can a vegan or vegetarian diet cause anaemia?
Vitamin B12 is found almost entirely in animal foods, so a vegan or strict vegetarian diet without supplementation can lead to B12 deficiency over time. The Australian Dietary Guidelines advise people following a vegan diet to take a vitamin B12 supplement. Your GP can advise on testing and supplementation.
How is vitamin B12 deficiency treated?
Treatment depends on the cause. Vitamin B12 deficiency may be treated with B12 injections or high-dose tablets, and where the problem is poor absorption (such as pernicious anaemia), injections are often used long term. Folate deficiency is usually treated with folic acid tablets and dietary changes. Your GP will tailor treatment to you.
Why is folate important in pregnancy?
Folate helps protect a developing baby against neural tube defects such as spina bifida. In Australia, women who are planning a pregnancy or are in the early stages are generally advised to take a folic acid supplement. Speak with your GP for advice suited to your situation.
Trusted Sources for Further Reading
- Healthdirect Australia — Vitamin B deficiency and Vitamin B12 blood test
- Healthdirect Australia — Anaemia
- Eat For Health (NHMRC) — Australian Dietary Guidelines
This article is for general information only and does not replace professional medical advice. The right tests and treatment differ from person to person. Please do not start supplements without guidance, as treating one deficiency while missing another can cause harm. If you have concerns about your health, please consult your GP.
