Low haemoglobin: causes, symptoms and what to do

When haemoglobin is below your report’s limit, it is usually called anaemia: your body gets less oxygen. The most common cause is a lack of iron, from heavy periods, a pregnancy or small blood losses. But not always: in Italy many people carry thalassaemia trait, known there as Mediterranean anaemia, and then iron usually does not help.

What low haemoglobin means

Haemoglobin carries oxygen from your lungs to the rest of your body. When it is low, your muscles and brain get less of it, and you tire sooner.

Below your report’s limit it is usually called anaemia. Below 11 it is called moderate anaemia, below 8 severe anaemia.

The number shows how low it is, not why. Finding that out takes other tests.

What causes low haemoglobin

The first is the most common.

• Too little iron: From heavy periods, a pregnancy, frequent blood donation or too little iron on your plate.
• Hidden blood loss: Small losses from the gut that you cannot see. In men and after menopause, they are the first thing doctors look for.
• Too little B12 or folate: Your body needs them to make red cells too. In this case the red cells are bigger than normal.
• Thalassaemia trait: Common in Italy, where it is called Mediterranean anaemia: haemoglobin is slightly low and red cells are small, but iron is usually not short.
• Inflammation and kidneys: Long-lasting inflammation, or kidneys that filter less, slow down the making of red cells.
• A lot of endurance sport: The blood gets diluted and the number can look low without real anaemia. Ferritin helps tell.

Symptoms

Mild anaemia often causes no symptoms. When it is more marked, you may notice:

• Tiredness that does not go away
• Shortness of breath when you exert yourself
• Pale skin
• Dizziness
• A racing heartbeat
• Cold hands and feet

These symptoms can have other causes too. And when anaemia comes on slowly the body adapts, so you can feel fine even with a low number.

Thalassaemia trait: why iron is not always the answer

In Italy many people are healthy carriers of thalassaemia, also called Mediterranean anaemia. It is an inherited trait: haemoglobin is normal or slightly low, red cells are small and ferritin is usually normal.

In this case iron does not help and does not raise haemoglobin. The sign: small but numerous red cells, with an MCV that is very low for how low the haemoglobin is. It is usually confirmed by haemoglobin electrophoresis, which separates the types of haemoglobin: it is not the same test as protein electrophoresis.

Being a healthy carrier usually causes no problems and needs no treatment. But it is worth knowing, so you do not take iron you do not need and, if you are planning a pregnancy, so your partner can be checked too.

Which tests to read alongside it

These tests help find the cause.

What your result means

The lower end of the scale, in g/dL.

• Below 8: Severe anaemia. Your blood carries much less oxygen than normal. Talk to a doctor today, even if you feel fine. If you are short of breath at rest, have chest pain or faint, call 112.
• 8 to under 11: Moderate anaemia. Your blood carries less oxygen, and you often feel tired. Talk to a doctor soon to find the cause.
• 11 up to your report’s limit, Women: usually 11 to under 12, Men: usually 11 to under 14: Low. It can be mild anaemia. Iron is usually behind it, sometimes an inherited trait. Check your ferritin and MCV too, and talk to your doctor to find the cause.
• Within your report’s limits, Women: usually 12 to 16, Men: usually 14 to 18: Normal. Your blood carries enough oxygen. But your iron store can already be low. In the Rosa report you also see whether you are in your optimal range.

How to raise your haemoglobin

First find the cause, because the treatment depends on it. Where to start:

• Start with the tests: your doctor reads haemoglobin together with ferritin and MCV.
• Do not take iron without checking your ferritin first: if you are not short of iron, it does not help.
• If the anaemia comes from a lack of iron, food alone is usually not enough: you need a supplement, with the dose and length set by your doctor.
• Iron tablets often make stools dark. If they are black like tar, or you feel weak or dizzy, call 112 or go to the emergency department.
• What to eat: iron from red meat, fish and shellfish is absorbed best. Legumes and leafy greens have iron too: eat them with citrus, kiwi or peppers, and keep tea and coffee away from meals.
• With thalassaemia trait iron does not help, unless you are short of it as well.
• With treatment, if iron was short, haemoglobin starts to rise within the first few weeks. Once it is back to normal, treatment usually continues for about three months to fill the store.

When to worry

Talk to a doctor if:

• Your haemoglobin is below your report’s limit, even slightly.
• You are a man, or a woman after menopause, and you are short of iron.
• You do not know why it is low.
• It is below 8: talk to a doctor today.
• You see black stools or blood in your stools: call 112 or go to the emergency department.
• You are short of breath at rest, have chest pain or feel faint: call 112 or go to the emergency department.

With Rosa, a haemoglobin below 11 is always flagged to a doctor, below 8 urgently.

Frequently asked questions

Haemoglobin at 9: what should I do? Talk to your doctor soon: at 9 it is called moderate anaemia, and the cause needs finding, usually starting with ferritin and MCV. With Rosa, below 11 the result is always flagged to a doctor.

Haemoglobin at 7 or 8: what are the risks? Below 8 it is called severe anaemia: your heart has to work harder. Talk to a doctor today, even if you feel fine, and at 8 as soon as possible. If you are short of breath at rest, have chest pain or faint, call 112. The cause can usually be found and treated.

Is low haemoglobin dangerous? Usually it is not an immediate danger. The most common kind, from a lack of iron, usually clears up with treatment. It becomes serious when it is very low, below 8, or when it drops fast because of blood loss: then you need a doctor straight away.

Can low haemoglobin be a sign of cancer? Usually not. In women before menopause the most common causes are periods, pregnancy and diet. In men and after menopause, if iron is short, doctors look first for blood loss from the stomach or gut. Sometimes that comes from a tumour, which is why anaemia should always be checked by a doctor.

Low haemoglobin in pregnancy: what to do? In pregnancy it drops a little because the blood gets more diluted, and the limit for anaemia is lower: 11 in the first and third trimester, a little less in the second. You also need a lot more iron: talk to your obstetrician, who decides whether and how to supplement.

Sources

• World Health Organization, guideline on haemoglobin cutoffs to define anaemia in individuals and populations. Geneva, 2024. PMID 38530913
• British Society of Gastroenterology, guidelines for iron deficiency anaemia in adults. Gut, 2021. PMID 34497146
• British Society for Haematology, guideline for the diagnosis and management of polycythaemia vera. British Journal of Haematology, 2019. PMID 30478826
• Kiss and colleagues, oral iron after blood donation and how long haemoglobin takes to recover. JAMA, 2015. PMID 25668261
• White and colleagues, testosterone therapy and secondary erythrocytosis. International Journal of Impotence Research, 2022. PMID 34987178