Haemoglobing/L
Oxygen-carrying capacity
Also known as: Hemoglobin, Hb, HGB
Typical optimal range
135–175 g/L
Female
A typical optimal range for adults is around 135–175 g/L, though reference intervals differ between men and women and vary between laboratories, so your result should always be interpreted against your own lab's ranges. These figures are indicative — the range printed on your own lab report is the definitive one for your results.
NICE guideline NG24 covers the diagnosis and management of anaemia in adults and provides the main clinical framework for interpreting low haemoglobin in UK practice.
What is Haemoglobin?
Haemoglobin (Hb) is the iron-containing protein packed inside red blood cells that binds oxygen in the lungs and carries it to every tissue in the body. It is produced in the bone marrow and requires adequate iron, vitamin B12, and folate to be made in sufficient quantities. Measuring haemoglobin concentration in a blood sample gives a direct picture of the blood's oxygen-carrying capacity, making it the primary marker used to identify and monitor anaemia.
What a high Haemoglobin means
A haemoglobin result above the laboratory's upper reference limit suggests the blood contains a higher than usual concentration of the protein, which can reflect several different underlying states and warrants a closer look rather than immediate concern.
- Dehydration. When plasma volume is reduced through insufficient fluid intake, vomiting, or heavy sweating, haemoglobin concentration rises artificially because the same number of red cells are suspended in less fluid. This is one of the most common and easily reversible causes of a mildly elevated result.
- Smoking. Carbon monoxide from cigarette smoke binds haemoglobin, reducing its oxygen-carrying efficiency. The body compensates by producing more red cells and haemoglobin, so smokers routinely have higher Hb values than non-smokers — a well-recognised physiological adaptation rather than a sign of good health.
- Polycythaemia vera or secondary polycythaemia. Persistent, significantly elevated haemoglobin may point to polycythaemia vera (a bone marrow condition) or secondary polycythaemia driven by chronic low oxygen states such as untreated sleep apnoea or long-standing lung disease. These require GP assessment to investigate further.
A single mildly elevated reading in an otherwise well person is often due to dehydration or the timing of the sample; a repeat test after adequate hydration usually clarifies the picture.
What a low Haemoglobin means
A haemoglobin below the laboratory's lower reference limit indicates anaemia — a reduced capacity to carry oxygen around the body — and identifying the underlying cause is an important step, as anaemia is a symptom rather than a diagnosis in itself.
- Iron-deficiency anaemia. The most common cause of low haemoglobin in the UK, iron deficiency can result from inadequate dietary intake, poor absorption (for example in coeliac disease), or ongoing blood loss such as heavy menstrual periods or gastrointestinal bleeding. Your GP will typically check iron stores (ferritin) and a full blood count alongside Hb.
- B12 or folate deficiency. Both vitamin B12 and folate are essential for red blood cell production; deficiency causes larger but fewer red cells and a characteristic pattern on the blood count. This is common in people with restrictive diets, older adults, or those with conditions affecting absorption such as pernicious anaemia or inflammatory bowel disease.
- Anaemia of chronic disease. Long-standing inflammatory or chronic conditions — including kidney disease, rheumatoid arthritis, and cancer — can suppress red blood cell production through multiple mechanisms, producing a mild to moderate anaemia that often improves when the underlying condition is treated.
Symptoms such as persistent fatigue, breathlessness, or palpitations alongside a low Hb should always prompt a GP review; even a modest fall in haemoglobin can be clinically significant if it represents a change from a previous result.
Should I be worried?
A single haemoglobin result slightly outside the reference range does not in itself mean something is seriously wrong, but it is worth taking seriously and discussing with your GP rather than ignoring, particularly if it is low. Your GP will usually look at the result alongside the rest of the full blood count — including red cell size, your white cell and platelet counts, and markers such as ferritin and B12 — to work out whether anaemia is present and what might be driving it. Symptoms like unexplained fatigue, shortness of breath, pale skin, or noticeable changes in your periods or bowel habits are important to mention at the same time, as they help direct investigation. A repeat test is often arranged to confirm a result before further steps are taken, so try not to worry unduly on the basis of a single reading.
What actually helps
While the right treatment for abnormal haemoglobin depends entirely on the underlying cause, several evidence-based lifestyle and dietary factors support healthy red blood cell production.
- Ensure adequate iron intake. Iron is the single most important nutrient for haemoglobin synthesis. The best-absorbed form (haem iron) is found in meat and fish; non-haem iron from plant foods is absorbed less efficiently but can be meaningfully improved by consuming it alongside vitamin C-rich foods.
- Support B12 and folate status. Both nutrients are essential for red cell production and are commonly low in people who eat little or no animal produce. If your diet is restricted, a supplement or dietary review with a health professional is a practical step, but do not self-treat with high-dose supplements without guidance from your GP.
- Address identified blood loss. If heavy menstrual bleeding or suspected gastrointestinal blood loss is contributing to low haemoglobin, managing the underlying cause — under medical guidance — is more effective than dietary changes alone. Do not delay speaking to your GP if you notice blood in your stool or a significant change in menstrual flow.
- Stay well hydrated. Because dehydration artificially concentrates the blood and raises haemoglobin readings, ensuring consistent fluid intake helps produce results that accurately reflect your true red cell status.
There is good supporting evidence that the following foods help maintain the nutrients needed for healthy haemoglobin production.
Red meat and liver
Among the richest sources of haem iron and vitamin B12, both of which are directly required for haemoglobin synthesis; modest, regular intake is well supported by evidence, though liver is advised in moderation and avoided in pregnancy due to high vitamin A content.
Oily fish and shellfish (especially clams and mussels)
Good sources of both haem iron and B12; mussels in particular are exceptionally iron-rich relative to their calorie content.
Legumes (lentils, chickpeas, kidney beans)
Among the best plant-based sources of non-haem iron and folate; combining them with vitamin C-containing foods in the same meal improves iron absorption.
Dark green leafy vegetables (spinach, kale, broccoli)
Provide non-haem iron and folate; spinach also contains vitamin C, though its oxalate content modestly limits iron absorption compared with other sources.
Fortified breakfast cereals
Many UK cereals are fortified with iron and B vitamins including folate and B12, making them a practical option for those with lower meat intakes; check labels as fortification levels vary.
Citrus fruit and peppers
Rich in vitamin C, which significantly enhances absorption of non-haem iron from plant foods when eaten at the same meal — an important pairing for those relying on plant-based iron sources.
Track your own Haemoglobin
Upload a lab PDF and Better Days trends Haemoglobin over time, flags it when it drifts, and suggests foods that help.
More in Blood Count
Sources & further reading
These are reputable UK health resources for further reading. This page is written to be consistent with their guidance but is not a substitute for them.
For information only — not medical advice, and not individually reviewed by a clinician. Reference ranges vary by lab and individual. Discuss any results with a qualified clinician before making changes.