Low haemoglobin (anaemia): common causes and the tests doctors ask for
Why haemoglobin can be low, which tests help find the cause, and why it is safer to find out the reason before starting treatment on your own.
What is haemoglobin?
Haemoglobin is the protein inside red blood cells that carries oxygen around the body. When the level is lower than expected for your age and sex, the result is called anaemia. Normal ranges differ between laboratories, so always compare your result with the range printed on your own report.
Symptoms people notice
Tiredness, pale skin, breathlessness on effort, headaches, a racing heartbeat or feeling dizzy can all go with anaemia. These symptoms are not specific. Many other conditions can cause them, so they are a reason to get tested rather than a diagnosis.
Common causes
- Not enough iron, from diet, heavy periods, pregnancy or slow blood loss.
- Low vitamin B12 or folate.
- Long-term conditions such as kidney disease or ongoing inflammation.
- Inherited conditions such as thalassaemia trait.
- Bone marrow problems, which are less common.
Tests a doctor may ask for
- A complete blood count (CBC), which shows haemoglobin, red cell size and the other blood cells.
- Iron tests such as ferritin.
- Vitamin B12 and folate levels.
- A blood film, where a specialist looks at the cells under a microscope.
- Further tests, depending on the first results.
Why the cause matters
Treatment depends on the reason. Iron suits iron deficiency, vitamin B12 suits a B12 deficiency, and some causes need other care from a doctor. Starting treatment without knowing the cause can hide the real problem.
When to seek urgent care
Severe breathlessness, chest pain, fainting or signs of heavy bleeding need emergency care straight away.
If you have a low haemoglobin result and would like it explained, you can book a new consultation.
Frequently asked questions
Is anaemia always caused by low iron?
No. Iron deficiency is common, but anaemia can also come from other vitamin deficiencies, long-term illness, inherited conditions, blood loss or problems in the bone marrow. That is why the cause needs to be found.
Can I start iron tablets without a test?
It is better to check first. Taking iron when it is not the cause can delay the right diagnosis, and some inherited conditions do not improve with iron.