Blood Tests for Anaemia: Finding the Cause

Anaemia means you have fewer healthy red blood cells, or less haemoglobin, than normal, so less oxygen reaches your body. It can make you feel tired and short of breath, give you heart palpitations, headaches or pale skin, or cause no symptoms at all and show up only on a routine blood test.

Anaemia is a sign rather than a diagnosis, so the most important question is why it has happened. This guide explains the main types of anaemia and which blood tests help find the cause, which test to book, what blood tests cannot show and when to get urgent help. For the numbers themselves, see our guides to haemoglobin levels and ferritin levels.

Test it in Chiswick: our Anaemia Check blood test costs £129, with your result explained in person by a practitioner. No GP referral needed. Book this test or call 020 4515 0000.

Quick answer

A full blood count confirms anaemia and shows the size of your red cells, which points to the likely cause. Small cells usually suggest iron deficiency, confirmed with ferritin and iron studies. Large cells can suggest vitamin B12 or folate deficiency, alcohol, liver or thyroid problems. Long-term inflammation can cause anaemia with normal or high ferritin, so CRP helps. NICE advises a coeliac blood test for unexplained iron, B12 or folate deficiency, and a stool test (FIT) through your GP for adults with iron deficiency anaemia.

Types of anaemia

• Iron deficiency anaemia: a common type. The NHS says heavy periods and pregnancy are very common causes, along with bleeding in the stomach or intestines and too little iron in the diet.
• Vitamin B12 or folate deficiency anaemia: the NHS says the most common cause of B12 deficiency in the UK is pernicious anaemia, an autoimmune condition that stops B12 being absorbed. Diet and some medicines, such as proton pump inhibitors and anticonvulsants, can also play a part.
• Anaemia of chronic disease: long-term inflammation from illnesses or infections blocks the body's access to its iron, even when stores are adequate. Kidney disease can also reduce red cell production.
• Haemolytic anaemia: less common. Red cells are destroyed faster than they are made, for example in inherited conditions such as sickle cell disease, or rarely because of medicines or infection. It needs specialist investigation.

Blood tests that can help

Full blood count (FBC)

The full blood count is the starting point. It measures your haemoglobin, to confirm whether you are anaemic, and the size of your red cells (mean cell volume, MCV). Small red cells most often point to iron deficiency. Large red cells have several causes: an NHS haematology pathway lists alcohol as the most common, followed by B12 or folate deficiency, liver disease, an underactive thyroid and some medicines. Our Full Blood Count costs £59. Read what a full blood count shows and our guide to MCV and MCH levels.

Ferritin and iron studies

Ferritin reflects your iron stores, and a low ferritin with anaemia confirms iron deficiency anaemia. However, ferritin is an acute phase protein, which means it rises with inflammation and can look normal even when iron stores are low. NHS laboratory guidance advises testing transferrin saturation when there is doubt. Book a Ferritin test (£49) or the Iron Status Check (£59), which adds serum iron, TIBC, transferrin and transferrin saturation.

Vitamin B12 and folate

B12 and folate are both needed to make healthy red cells. The NHS notes that B12 deficiency can cause pins and needles, muscle weakness, memory problems and changes in mood, sometimes before anaemia develops, and that some effects can become permanent without prompt treatment. Book a Vitamin B12 test (£49) and a Folate test (£49). Our guides to B12 levels and folate levels explain the results.

CRP: looking for inflammation

C-reactive protein (CRP) rises with inflammation. A raised CRP alongside anaemia can point towards anaemia of chronic disease, and it also tells your practitioner that a normal ferritin may be hiding low iron stores. Our CRP test costs £49, or the Inflammation Check (£79) combines a full blood count, ferritin, CRP and ESR.

Coeliac antibodies

Coeliac disease can stop the gut absorbing iron, B12 and folate properly. NICE recommends offering a coeliac blood test to anyone with unexplained iron, vitamin B12 or folate deficiency. The test is only accurate if you are eating gluten, so do not cut it out before testing. Our Coeliac Antibody Check (£99) measures tTG IgA and IgG antibodies.

Tests we do not offer

If haemolysis or a bone marrow problem is suspected, your GP or a haematologist may arrange specialist tests such as a reticulocyte count or a blood film. We do not offer a reticulocyte count at our clinic.

Which test should I book?

• A focused start: Iron Status Check, £59. Ferritin, serum iron, TIBC, transferrin and transferrin saturation. Useful if you already know you are anaemic, for example from a recent GP result, as it does not measure haemoglobin.
• A broader picture: Full Blood Count, £59. Haemoglobin, red cell count, haematocrit, MCV, MCH, MCHC, white cells and platelets. It confirms anaemia and the red cell size, but not the cause.
• The fullest view: Anaemia Check, £129. A full blood count plus ferritin, iron studies, vitamin B12, folate and CRP, covering the common causes in one sample.

Add the Coeliac Antibody Check if iron, B12 or folate turns out to be low without a clear reason.

What blood tests cannot tell you

Blood tests can show that you are low in iron, but not where the iron has gone. NHS laboratory guidance notes that in adult men and postmenopausal women, blood loss from the gut is the most common cause of iron deficiency anaemia. NICE guidance on suspected bowel cancer advises a faecal immunochemical test (FIT), a stool test for hidden blood, to guide referral for adults with iron deficiency anaemia, and for anyone aged 60 or over with anaemia even without iron deficiency. Your GP may also test your urine for blood or refer you for a gastroscopy or colonoscopy.

Heavy periods are a very common cause in women. The NHS describes periods as heavy if you need to change your pad or tampon every 1 to 2 hours or pass clots larger than about 2.5cm, and your GP can look for an underlying cause. Haemolytic anaemia, kidney-related anaemia and bone marrow problems need medical assessment beyond the tests listed here. Our practitioner can provide a GP feedback report so your results can be followed up.

When to see a GP urgently

Ask for an urgent GP appointment or call NHS 111 if:

• you are more short of breath than usual, or you have heart palpitations
• your poo is black or dark red, or you have bloody diarrhoea
• you have pins and needles, muscle weakness, vision problems or memory problems that could be due to B12 deficiency, as the NHS says this needs diagnosing and treating as soon as possible

Call 999 or go to A&E if you have severe difficulty breathing, your lips or skin turn very pale, blue or grey, you are bleeding heavily and it will not stop, there is a lot of blood (for example the toilet water turns red), or you have chest pain that spreads to your arms, neck, jaw or back, or comes with sweating, feeling sick or shortness of breath.

Frequently asked questions

Which blood test shows the cause of anaemia?

No single test does. A full blood count shows the red cell size, which narrows the possibilities, then ferritin, iron studies, B12, folate and CRP usually identify the most common causes.

Can you be iron deficient without being anaemic?

Yes. Iron deficiency without anaemia is recognised, and NHS laboratory guidance advises a low threshold for investigating iron deficiency without anaemia in men and postmenopausal women.

Why do I need a coeliac test for anaemia?

Coeliac disease damages the lining of the small intestine and reduces absorption of iron, B12 and folate. NICE recommends testing for it whenever these deficiencies are unexplained.

Why has my GP asked for a stool sample?

A FIT test looks for tiny amounts of blood in your poo. NICE recommends it to guide whether you need a bowel investigation if you have iron deficiency anaemia.

When should I retest after starting iron?

The NHS says your GP may repeat blood tests over the next few months to check your iron level is recovering, and that iron tablets are usually taken for about 6 months. Your practitioner can advise on timing.

Anaemia blood tests in Chiswick

Omnia Lifestyle is at 8 to 9 Bedford Corner, The Avenue, Chiswick, London W4 1LZ, a short walk from Turnham Green station (District line; Piccadilly line trains stop there early morning and late evening only) and served by buses 94, E3 and 272. Limited parking is available on request when you book. Every clinic test price includes your sample taken at the clinic, analysis at the Randox accredited laboratory, a practitioner review of your result with you, and a GP feedback report on request. You do not need a GP referral, and most results are back within a few working days.

Useful links: book the Anaemia Check or a Full Blood Count, add a Ferritin test, or compare every blood test and price. Our guides to haemoglobin levels and ferritin levels explain what your numbers mean, and our FAQ on blood tests for tiredness covers other causes of fatigue.

This article is general information, not medical advice. Discuss your results with your GP or practitioner.