Hemoglobin (Hb)
Haemoglobin is the oxygen-carrying protein in red blood cells. This test measures haemoglobin levels to detect anaemia, polycythemia, or monitor blood loss. No fasting required.
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What the Hemoglobin (Hb) test tells you
Haemoglobin is the iron-containing protein packed inside red blood cells that binds oxygen in the lungs, carries it through the circulation, and releases it where the tissues need it. Measuring it is the most direct way of asking how much oxygen-carrying capacity your blood actually has. Because red cells are constantly being made in the bone marrow and constantly being retired, the value reflects the balance between production, survival and loss at the moment the sample was taken.
A low haemoglobin is what doctors call anaemia. It is a finding rather than a diagnosis, and its importance lies entirely in the reason behind it. Iron deficiency is the most common explanation worldwide and is often the visible end of slow, unnoticed blood loss. Deficiency of vitamin B12 or folate interrupts red cell production in a different way and produces larger cells. Chronic kidney disease reduces the hormonal signal that instructs the marrow to work; long-standing inflammation locks iron away where the marrow cannot use it; and inherited conditions such as thalassaemia or sickle cell disease alter the haemoglobin molecule itself. Each of these causes tiredness and breathlessness in much the same way, which is why the number alone never settles the question.
A raised haemoglobin is interpreted with equal care. Dehydration is the commonest reason, and it does not mean more red cells at all: the same cells are simply suspended in less plasma, so the concentration reads high. Genuine increases follow from anything that leaves the tissues short of oxygen over time, including smoking, chronic lung disease, untreated sleep apnoea and prolonged life at altitude, and less commonly from a bone marrow disorder that overproduces red cells. Your doctor will look at the red cell indices, iron studies and the rest of the blood count before deciding what a result means for you.
Fundamental test for assessing oxygen-carrying capacity of blood. Essential in evaluating fatigue, pallor, dizziness, and monitoring conditions affecting red blood cells.
- Detecting anaemia
It is the primary measurement used to establish whether the oxygen-carrying capacity of your blood is reduced.
- Explaining fatigue and breathlessness
Persistent tiredness, pallor and breathlessness on mild exertion are among the commonest reasons this test is requested.
- Assessing blood loss
Heavy periods, surgery and hidden bleeding in the gut are all followed by measuring haemoglobin over time.
- Tracking treatment response
Once iron, vitamin B12 or folate treatment begins, repeat measurements show whether it is working.
Reasons your doctor may request the Hemoglobin (Hb) test
Your doctor may order this test for any of the reasons below. Some are routine checks, others follow specific symptoms or an earlier result.
Tiredness, breathlessness & pallor
- You feel persistently tired, breathless on mild exertion, or look pale.
Blood loss
- You have heavy menstrual periods or another recognised source of ongoing blood loss.
Treatment, surgery & chronic disease
- You are being assessed before surgery or before donating blood.
- Iron, vitamin B12 or folate treatment has been started and its effect needs checking.
- You have a chronic condition such as kidney disease that commonly causes anaemia.
A result in the "Low" g/dL band is anaemia, which is a finding to investigate rather than a diagnosis. Iron deficiency is the commonest cause, followed by blood loss including bleeding hidden in the gut, vitamin B12 or folate deficiency, chronic kidney disease, long-standing inflammation, and inherited conditions such as thalassaemia. A "Normal" g/dL result reflects healthy oxygen-carrying capacity, though hydration shifts the figure in both directions without any change in true red cell mass. A "High" g/dL reading is more often dehydration, smoking, life at high altitude, chronic lung disease or untreated sleep apnoea than a marrow disorder. Haemoglobin alone does not reveal the cause, and thalassaemia trait can look much like iron deficiency here. Your doctor reads it with red cell indices, iron studies, your symptoms and your history, and judges recovery on the trend.
Medically reviewed by Dr Nirupama Sabhapathy
Ranges are a guide: your physician interprets your result alongside your symptoms and history.
What a higher result can point to
- Dehydration, which concentrates the blood without any true increase in red cells.
- Smoking, which raises red cell production to compensate for reduced oxygen delivery.
- Chronic lung disease or untreated sleep apnoea, where low oxygen drives the bone marrow.
- Prolonged life at high altitude.
- Polycythaemia vera and other bone marrow disorders that overproduce red cells.
- Testosterone therapy or the misuse of erythropoietin.
What a lower result can point to
- Iron deficiency, the most common cause worldwide.
- Acute or slow chronic blood loss, including bleeding hidden within the gut.
- Vitamin B12 or folate deficiency, which disrupts red cell production.
- Chronic kidney disease, which reduces the hormone signal driving the bone marrow.
- Long-standing inflammation or infection, which locks iron away from the marrow.
- Inherited conditions such as thalassaemia or sickle cell disease.
These are possibilities, not diagnoses. A single value outside the reference range is interpreted alongside your symptoms, history and other tests: your doctor decides what it means for you.
What this test cannot tell you
- Haemoglobin alone does not reveal the cause of anaemia; red cell indices and iron studies are usually needed alongside it.
- Hydration shifts the value in both directions without any change in the true red cell mass.
- Thalassaemia trait and iron deficiency can look similar on haemoglobin alone and need further tests to separate.
- Posture and a prolonged tourniquet during sampling can nudge the value slightly.
Risks of the blood draw
- Mild bruising or brief soreness where the needle went in.
- Occasional lightheadedness, which settles after a few minutes of rest.
- Bleeding or infection at the site, which is rare with sterile single-use equipment.
- 1Haemoglobin is the iron-containing protein that carries oxygen from the lungs to the tissues.
- 2A low value is called anaemia, which is a finding to investigate rather than a diagnosis in itself.
- 3A high value is more often dehydration or a response to low oxygen than a marrow disorder.
- 4It is interpreted alongside red cell size, iron studies and the rest of the blood count.
- 5Recovery after treatment is judged on the trend rather than on any single reading.
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Frequently Asked Questions
Everything you need to know about the Hemoglobin (Hb) test. Can't find what you're looking for?
Talk to our team→Our laboratory reports 12 to 17 g/dL as normal. Below 12 g/dL is reported as low, which is anaemia, and above 17 g/dL as high. Hydration shifts the figure in both directions without any change in your true red cell mass, so drink normally before the test and read borderline values with that in mind.
Low haemoglobin means less oxygen reaches the tissues, so the usual symptoms are tiredness, pale skin, dizziness and breathlessness on exertion. A slow fall can produce surprisingly few symptoms because the body adapts, so anaemia is often found on a routine test. Anaemia is a finding to investigate rather than a diagnosis, and your doctor looks for its cause.
Yes. Thalassaemia trait can lower haemoglobin slightly and, on haemoglobin alone, look much like iron deficiency. Inherited haemoglobin conditions are common in families from the Gulf region, so this matters here. Red cell indices, iron studies and further tests separate the two, which is important because the next steps are different.
Haemoglobin tells you whether anaemia is present but not why. A complete blood count adds red cell size and other indices that point towards iron deficiency, vitamin B12 or folate deficiency or a thalassaemia trait, and iron studies are often added. For anything beyond a quick check or tracking a known condition, your doctor will usually want the fuller picture.
Yes. Heavy periods are a common source of slow, ongoing blood loss, which drains iron stores and leads to iron deficiency, the commonest cause of a low haemoglobin. If your haemoglobin is low and your periods are heavy, your doctor will usually check iron stores and may look at the bleeding itself, since correcting both is what brings the level back up.
No. Iron deficiency is the most common cause, but vitamin B12 or folate deficiency, chronic kidney disease, long-standing inflammation, blood loss and inherited haemoglobin disorders all lower it too. The red cell indices and iron studies are used to tell them apart.
The most frequent explanation is simple dehydration, which concentrates the blood without changing the number of red cells. Smoking, sleep apnoea and living at altitude also raise it genuinely. A persistently high value that cannot be explained this way is investigated further.
The bone marrow responds before the haemoglobin does. Young red cells appear in the circulation within days, while a measurable rise in haemoglobin takes rather longer, so your doctor will usually wait some weeks before repeating the test.
They are closely related but not identical. Haemoglobin measures the oxygen-carrying protein itself, while haematocrit measures the proportion of blood volume occupied by red cells. They usually move together, and both are affected by hydration.
No, fasting is not required and you can take your usual medicines and supplements. Drink normally beforehand, because dehydration can make haemoglobin read falsely high. If you have had a recent transfusion, tell the team, since donated cells influence the result for some weeks.
The haemoglobin test is AED 25, including a physician-reviewed report, with results usually within 24 hours. Home collection anywhere in Dubai is free when your order reaches AED 300 or includes a package; below that, a AED 100 home collection fee applies (AED 50 for a lab walk-in).