Haemoglobin — often written as hemoglobin in American English and abbreviated as Hb or Hgb on laboratory reports — is one of the most clinically important measurements in routine blood testing. If you have recently received a blood test result and wondered what your Hb or Hgb figure means, whether your haemoglobin level is normal, or what it could mean if your result falls outside the reference range, this guide explains everything you need to know.
This article covers what haemoglobin is, how it is measured, how to interpret reference ranges and when it may be appropriate to discuss an unexpected result with a healthcare professional.
What Is Haemoglobin?
Haemoglobin is a protein found inside red blood cells. Its primary function is to carry oxygen from the lungs to the tissues and organs throughout your body, and to transport carbon dioxide — a waste product of metabolism — back to the lungs so it can be exhaled.
Each haemoglobin molecule contains iron-rich subunits called haem groups. It is the iron within these groups that binds to oxygen, giving oxygenated blood its characteristic bright red colour. Without adequate haemoglobin, your body's tissues cannot receive a sufficient oxygen supply, which is why haemoglobin is considered a fundamental marker of health and wellbeing.
Because haemoglobin is so central to oxygen transport, measuring its concentration in the blood provides clinicians with important information about how effectively your blood is performing one of its most essential roles.
What Do Hb and Hgb Mean on a Blood Test?
When you look at a blood test report, you may see your haemoglobin result labelled as Hb, Hgb or Haemoglobin. These are simply different abbreviations and spellings used to describe the same measurement:
Both haemoglobin and hemoglobin refer to exactly the same protein. The difference is purely a matter of spelling convention. When people search for information about hemoglobin online, they are looking for precisely the same information as those searching for haemoglobin. Throughout this article, we use the British spelling haemoglobin as standard UK medical practice, while acknowledging that hemoglobin is the predominant spelling in US English.
Related Test
Full Blood Count
Complete blood analysis • Same-day appointments • UKAS-accredited lab
What Is a Haemoglobin Blood Test?
A haemoglobin test measures the concentration of haemoglobin in your blood, typically expressed in grams per decilitre (g/dL) or occasionally grams per litre (g/L).
In most cases, haemoglobin is not tested in isolation. It is one of the key measurements included within a full blood count (FBC) — a panel of tests that examines different components of the blood, including red blood cells, white blood cells and platelets. The full blood count is one of the most commonly requested blood tests in both NHS and private healthcare settings.
A haemoglobin test or full blood count may be requested for a wide range of reasons, including:
If you are considering a private full blood count that includes haemoglobin measurement, you can find further information on the full blood count test page at Private Blood Tests London.
What Is a Normal Haemoglobin Level?
Understanding what a "normal" haemoglobin level means requires some important context. Reference ranges — the figures used to define what is considered normal — vary between laboratories, and also differ according to age, sex and certain physiological circumstances such as pregnancy.
There is no single universal normal haemoglobin value that applies to every person. Always compare your result with the reference range provided by the specific laboratory that processed your sample.
That said, the following approximate reference ranges are consistent with NHS guidance and widely used UK clinical practice:
| Group | Approximate Haemoglobin Reference Range |
|---|---|
| Adult men | 130–170 g/L (13.0–17.0 g/dL) |
| Adult women (non-pregnant) | 120–160 g/L (12.0–16.0 g/dL) |
| Pregnant women | Varies; generally lower thresholds apply |
| Children | Varies considerably by age |
Important: These ranges are provided for general educational purposes only. Individual laboratory reference ranges may differ slightly. Always refer to your own laboratory report and consult a healthcare professional for personalised interpretation.
A result that falls within the reference range provided by your laboratory is generally considered within the expected range for that population group. However, a result within the reference range does not automatically rule out an underlying health concern, and a result slightly outside the range does not necessarily indicate a serious problem. Context, symptoms and medical history all matter.
What Does a Low Haemoglobin Result Mean?
A haemoglobin result below the lower limit of your laboratory's reference range may be described as low haemoglobin or, in clinical terms, a reduced haemoglobin concentration. This is one of the markers associated with anaemia — a term that describes a state in which the blood's capacity to carry oxygen is reduced.
However, it is important to understand that:
Some of the factors and conditions that may be associated with low haemoglobin include:
A healthcare professional will consider all of these possibilities alongside your full clinical picture before drawing any conclusions. A low haemoglobin result is not confirmation of anaemia, nor does it confirm its cause without further assessment.
What Does a High Haemoglobin Result Mean?
A haemoglobin level above the upper limit of your laboratory's reference range is described as elevated or high haemoglobin. While less commonly discussed than low haemoglobin, a raised result also warrants careful interpretation.
Possible associations with elevated haemoglobin include:
As with low haemoglobin, a single elevated result cannot confirm any of these possibilities. High haemoglobin requires interpretation alongside other clinical information, and a healthcare professional should be consulted if your result falls above the reference range, particularly if you are experiencing symptoms.
Haemoglobin and Red Blood Cells: Understanding the Difference
Haemoglobin is often confused with the red blood cell (RBC) count, but these are two distinct measurements. Understanding the difference helps you make sense of your full blood count results.
It is entirely possible to have a normal red blood cell count but a reduced haemoglobin level, or vice versa. This is why the full blood count provides a more complete picture than any single measurement. A clinician will often look at several of these values together before reaching a conclusion.
Factors That Can Affect Haemoglobin Results
A number of factors — beyond underlying medical conditions — can influence your haemoglobin level and the way your result should be interpreted:
Informing your clinician or testing provider about any relevant factors before or at the time of testing can assist with accurate interpretation.
How Is a Haemoglobin Test Performed?
A haemoglobin test is performed using a standard venous blood sample, most commonly taken from a vein in the arm. The procedure is straightforward:
1. A healthcare professional cleans the skin at the sampling site.
2. A small needle is used to draw a blood sample into a collection tube.
3. The sample is labelled and sent to an accredited laboratory for analysis.
4. Your haemoglobin concentration — along with other full blood count measurements — is reported on a laboratory results sheet.
The process is generally quick and well tolerated. You do not usually need to fast before a haemoglobin test alone, although if additional tests are being requested alongside it, fasting instructions may apply. Always check with your testing provider for specific preparation guidance.
If you would like to explore private blood testing options in London, the health screening page at Private Blood Tests London provides an overview of available tests. You can also review blood test prices or book an appointment online.
Understanding Your Results
Receiving a haemoglobin result is the beginning of the interpretation process, not the end. A result on its own — whether within, above or below the reference range — tells only part of the story.
Effective interpretation considers:
A healthcare professional is best placed to interpret haemoglobin results within this broader context. If you are unsure about your results, or if your report indicates an out-of-range value, discussing this with your GP or a qualified clinician is always the appropriate next step.
When Should You Seek Medical Advice?
If your haemoglobin result is outside the reference range provided by your laboratory, it is sensible to discuss this with a healthcare professional, even if you feel well. Many people with abnormal haemoglobin results have no obvious symptoms, making routine testing a valuable tool.
You should seek prompt medical advice if you experience:
If you are experiencing severe chest pain, significant difficulty breathing or any symptom that concerns you urgently, contact 999 or attend your nearest emergency department without delay.
For concerns that are not urgent, your GP is the most appropriate first point of contact. Private blood testing can be a useful tool for proactive health monitoring, but it complements — and does not replace — appropriate medical care. You can find information about private blood test options at Private Blood Tests London.
Frequently Asked Questions
What is haemoglobin?
Haemoglobin is a protein found inside red blood cells. It carries oxygen from the lungs to the body's tissues and transports carbon dioxide back to the lungs. It is also the component that gives blood its red colour.
What do Hb and Hgb mean on a blood test?
Hb and Hgb are abbreviations for haemoglobin. Hb is commonly used in UK laboratory reports; Hgb is an alternative abbreviation sometimes seen in international or US-based reporting systems. Both refer to the same measurement.
What is the difference between haemoglobin and hemoglobin?
There is no clinical difference. Haemoglobin is the standard British English spelling, while hemoglobin is the American English spelling. Both describe the same protein.
What does a haemoglobin blood test measure?
It measures the concentration of haemoglobin protein in your blood, typically expressed in grams per decilitre (g/dL) or grams per litre (g/L).
Is haemoglobin measured as part of a full blood count?
Yes. Haemoglobin is one of the primary measurements within a full blood count (FBC), which also includes red blood cell count, white blood cell count, platelet count, haematocrit and other markers.
What is a normal haemoglobin level?
Reference ranges vary by laboratory, age and sex. As a general guide, many UK laboratories use approximately 130–170 g/L for adult men and 120–160 g/L for adult women. Always use your own laboratory's reference range and discuss results with a healthcare professional.
What is the normal Hb count?
The normal Hb count depends on your sex, age and the laboratory that analysed your sample. In general terms, for adult men approximately 13.0–17.0 g/dL and for non-pregnant adult women approximately 12.0–16.0 g/dL are widely cited ranges, though individual laboratory ranges may differ.
What does a low haemoglobin result mean?
A low haemoglobin result means the concentration of haemoglobin in your blood is below the lower reference limit for your group. It is associated with conditions such as anaemia but can have several possible causes, including iron deficiency, vitamin deficiency, chronic illness or blood loss. A healthcare professional should interpret the result in context.
What does high haemoglobin mean?
High haemoglobin means your concentration is above the upper reference limit. This can be associated with dehydration, smoking, high-altitude living, certain chronic conditions or, less commonly, a blood disorder called polycythaemia vera. Like any abnormal result, it requires professional interpretation.
Can a haemoglobin result diagnose anaemia?
No. A low haemoglobin result is one of the markers associated with anaemia, but anaemia is a clinical finding with multiple potential causes. Diagnosis requires a healthcare professional to consider the full blood count, additional tests, symptoms and medical history together.
What is the difference between haemoglobin and red blood cell count?
Haemoglobin measures the concentration of haemoglobin protein in the blood. Red blood cell count measures the number of red blood cells per unit volume. Both are measured in a full blood count, and they can move independently of one another — which is why both are assessed together.
When should I seek advice about an abnormal haemoglobin result?
You should discuss any out-of-range haemoglobin result with a healthcare professional, even if you feel well. If you are experiencing significant fatigue, breathlessness, pallor, palpitations or dizziness, seek prompt medical advice. For any severe or rapidly worsening symptoms, contact 999 or attend an emergency department immediately.
Medical References
1. NHS. *Full blood count (FBC)*. Available at: https://www.nhs.uk/conditions/blood-tests/ [Accessed October 2026]
2. NHS. *Anaemia — iron deficiency anaemia*. Available at: https://www.nhs.uk/conditions/iron-deficiency-anaemia/ [Accessed October 2026]
3. NICE. *Anaemia — iron deficiency. CKS*. Available at: https://cks.nice.org.uk/topics/anaemia-iron-deficiency/ [Accessed October 2026]
4. British Journal of Haematology. *Guidelines for the diagnosis and treatment of cobalamin and folate disorders*. BJH, 2014.
5. World Health Organization. *Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity*. WHO/NMH/NHD/MNM/11.1. Geneva: WHO, 2011.
6. Bain BJ, Bates I, Laffan MA. *Dacie and Lewis Practical Haematology*. 12th ed. Elsevier, 2017.
7. Marks PW. *Approach to anaemia in the adult and child*. In: Hematology: Basic Principles and Practice, 7th ed. Elsevier, 2018.