Haemoglobin
Haemoglobin (Hb)
What this test measures
Haemoglobin is a protein in your red blood cells that carries oxygen around your body. This test checks if you have enough red blood cells to carry oxygen to your organs and tissues.
Understanding the numbers
Typical range: Men: 130-180 g/L | Women: 115-165 g/L
Pregnant women may have slightly lower normal ranges. Ranges can vary slightly between laboratories.
- Severe anaemia: 40–80 g/L
- Moderate anaemia: 80–100 g/L
- Mild anaemia: 100–115 g/L
- Normal (women): 115–165 g/L
- Upper overlap (men): 165–180 g/L
- High: 180–200 g/L
Key numbers
- 80 g/L — Severe anaemia — consider urgent assessment
- 115 g/L — Women — lower limit of normal
- 130 g/L — Men — lower limit of normal
- 70 g/L — Very low — transfusion threshold commonly used
UK reference ranges (NICE anaemia guidance and typical lab ranges). Transfusion thresholds are clinician decisions based on symptoms, cause, and co-morbidities; 70 g/L is a commonly used threshold in stable patients (restrictive strategy).
Ranges can vary slightly between laboratories — your report may show slightly different numbers. This page does not read or interpret your result; your GP looks at it alongside your history and other tests.
What a higher-than-normal result can mean
- Your blood is thicker than normal with more red blood cells
- Can be caused by dehydration, smoking, or living at high altitude
- Sometimes linked to lung or heart conditions
- Rarely, it can be a sign of a blood disorder
When not to wait
Severe anaemia or heavy bleeding can become an emergency quickly.
- Chest pain, especially on exertion
- Breathlessness at rest or when lying flat
- Fainting or near-fainting
- Vomiting blood or passing black tarry stools
- A racing or irregular heartbeat
- Very pale skin, cold hands and feet, looking 'washed out'
- Known severe anaemia getting any of these symptoms
Call NHS 111 for urgent advice, or 999 if someone is seriously unwell.
Questions you could ask your GP
- What is causing my anaemia, and do I need further tests?
- Should I take iron supplements, and for how long?
- Could my diet be contributing to my low haemoglobin?
- When should I have my haemoglobin rechecked?
Example stories
These are made-up examples to show how results are talked about in real appointments. They are not real patients.
Heavy periods, chronically tired
Kiara had been tired for months. Her haemoglobin was 96 g/L, her MCV was small (74 fL), and her ferritin was 6. She had heavy periods and no other symptoms.
What the GP said: “This is iron deficiency anaemia, almost certainly from your periods. I'll start ferrous fumarate and we'll talk about treatment options for heavy periods. We'll recheck your bloods in three months.”
What happened next: Kiara started iron tablets and was referred to gynaecology. After a Mirena coil and six months of iron, her haemoglobin was 132 and ferritin 48.
Heavy periods are one of the most common causes of iron deficiency anaemia in women, and one of the most treatable. Iron tablets replace the iron; treating the blood loss stops it coming back.
Weight loss, tired, dark stools
Raymond had lost 4 kg, was short of breath on stairs, and his stools had been black for two weeks. His haemoglobin was 72 g/L with a low MCV.
What the GP said: “This is severe iron deficiency anaemia, and black stools suggest bleeding in the gut. I'm admitting you to hospital today for urgent investigation — you'll need an upper and lower GI endoscopy.”
What happened next: Hospital found a bleeding stomach ulcer from long-term ibuprofen use. It was treated, Raymond received two units of blood, and the ibuprofen was stopped. Twelve weeks on iron, his haemoglobin was 128.
Iron deficiency anaemia in older adults should always be investigated to find the source — especially with weight loss or dark stools. Bleeding ulcers and bowel cancers can present this way and need catching early.
Numbness in feet, sore tongue
Nalini's haemoglobin was 104 g/L but her MCV was high (108 fL). Her B12 was 98 pmol/L and her intrinsic factor antibodies were positive. She had numb toes and a red sore tongue.
What the GP said: “This is pernicious anaemia — your body cannot absorb vitamin B12 properly. Treatment is B12 injections, every other day to start with, then every three months for life.”
What happened next: Nalini had loading-dose B12 injections and her haemoglobin rose to 126 within three months. Her tongue healed and the foot numbness gradually improved.
Anaemia with large red cells (high MCV) points towards B12 or folate deficiency rather than iron. Pernicious anaemia needs lifelong B12 injections, not tablets — tablets don't get absorbed in this condition.
Smoker, dizzy, raised haemoglobin
Peter's haemoglobin was 195 g/L. He smoked 20 a day, had high blood pressure, and had been feeling dizzy and flushed.
What the GP said: “A high haemoglobin like this is called polycythaemia. Smoking is the most likely cause, but we need to rule out a bone marrow condition called polycythaemia vera. I'll check your JAK2 gene and refer to haematology.”
What happened next: JAK2 was positive — Peter had polycythaemia vera. He stopped smoking, started aspirin and venesection (removing a unit of blood every few months), and his haemoglobin came down to 160.
High haemoglobin is less common than low, but worth investigating. Smoking, chronic lung disease and sleep apnoea are common causes; a rarer cause is polycythaemia vera — a bone marrow condition that raises clot risk and needs treatment.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.