Haemoglobin levels: normal range, anaemia types, and what results mean

Haemoglobin is what makes blood red — but its role is far more consequential than colour. This iron-containing protein, packed inside red blood cells, binds oxygen in the lungs and releases it in the tissues where it is needed for cellular respiration. When haemoglobin falls too low, tissues experience hypoxia: not enough oxygen reaches the muscles, brain, and organs. The result is the familiar cluster of symptoms — persistent fatigue, breathlessness on mild exertion, pallor, and headaches.

Anaemia — defined as haemoglobin below the reference threshold for a person’s age, sex, and physiological state — is among the most prevalent laboratory abnormalities worldwide. The WHO estimates that over a quarter of the global population is affected, with iron deficiency as the dominant cause. Critically, anaemia is not a standalone diagnosis but a signal pointing to an underlying process: iron depletion, a chronic illness, a nutritional gap, or a bone marrow problem. That is why haemoglobin is almost never interpreted in isolation; it is read in context with the other indices on a complete blood count (CBC).

The WHO updated its haemoglobin thresholds in 2024. These revised cutoffs are the current clinical reference standard.

What haemoglobin is

Haemoglobin is a complex quaternary protein consisting of four globin chains, each containing an iron-containing haem group. It is that haem iron which binds oxygen molecules in the pulmonary capillaries and releases them in peripheral tissues — a reversible reaction that repeats with every circulation of a red blood cell.

Effective haemoglobin synthesis requires three key nutritional cofactors: iron, vitamin B12, and folate. A deficiency in any one of them impairs red blood cell production and leads to a fall in haemoglobin. Red blood cells themselves live for approximately 120 days, after which they are broken down in the spleen and liver; the iron is salvaged and recycled by the bone marrow.

One important point: haemoglobin is only one number in the full blood picture. Alongside it, the CBC provides MCV (mean corpuscular volume), MCH (mean corpuscular haemoglobin), MCHC, and the red cell count. These indices indicate what type of anaemia is present before any iron studies are even sent off.

Normal haemoglobin range

The values below correspond to the WHO 2024 updated thresholds. Your laboratory may report slightly different reference limits depending on the measurement method and local conventions — but the WHO figures represent the internationally accepted standard for diagnosing anaemia.

Group	g/L	g/dL
Men (≥15 years)	130–170	13.0–17.0
Non-pregnant women (≥15 years)	120–150	12.0–15.0
Pregnant — 1st and 3rd trimester	≥110	≥11.0
Pregnant — 2nd trimester	≥105	≥10.5
Children 5–11 years	≥115	≥11.5
Children 12–14 years	≥120	≥12.0

Several factors legitimately shift haemoglobin outside these ranges:

Altitude. People living above 1000 m have physiologically higher haemoglobin — the body compensates for lower atmospheric oxygen pressure by producing more red cells. The WHO publishes correction factors for different elevations.
Smoking. Carbon monoxide binds haemoglobin and reduces its effective oxygen-carrying capacity. In response, the body produces more red cells, raising haemoglobin by roughly 3–5 g/L. This is a compensatory reaction to a toxin, not a sign of health.
Athletes. Highly trained individuals often sit at the upper end of the normal range as a physiological adaptation to sustained aerobic demand.

Low haemoglobin: types of anaemia

Anaemia is not a single condition. The simplest classification uses MCV — the average size of a red blood cell — as its organising principle. MCV appears on every CBC report and gives the clinician an immediate working hypothesis about the cause before any iron studies return.

Microcytic anaemia (MCV <80 fL)

Small red blood cells suggest the bone marrow lacks the raw material to fill cells with haemoglobin properly.

Iron-deficiency anaemia — the most common form globally. Iron stores fall first: ferritin drops long before haemoglobin does. Once stores are exhausted, red cells become smaller and paler (hypochromic), and MCV and MCH fall together with haemoglobin.
Thalassaemia — an inherited defect in globin chain synthesis. MCV is characteristically low even when iron stores are normal or elevated; ferritin is unhelpful here, and haemoglobin electrophoresis or genetic testing is required.
Anaemia of chronic disease — in prolonged inflammatory states (rheumatoid arthritis, inflammatory bowel disease, malignancy), iron becomes sequestered in storage and is not available for haemoglobin synthesis. Anaemia can be microcytic or normocytic.

Normocytic anaemia (MCV 80–100 fL)

Normal-sized cells, but fewer of them or with a shortened lifespan.

Acute blood loss — circulating volume falls faster than the marrow can replenish red cells.
Haemolysis — premature destruction of red cells from autoimmune, hereditary, or drug-induced causes.
Early chronic kidney disease (CKD) — impaired renal function reduces erythropoietin production, the hormone that drives red cell synthesis. Interested in the kidney angle? See the article on creatinine and eGFR.
Anaemia of chronic disease (frequently normocytic, especially in the early phase).

Macrocytic anaemia (MCV >100 fL)

Abnormally large red cells signal disordered cell maturation in the bone marrow.

Vitamin B12 deficiency — the most common macrocytic cause. Without B12, bone marrow precursors cannot divide normally and are released as oversized, immature cells.
Folate deficiency — identical mechanism to B12, but different risk factors: inadequate dietary intake, pregnancy, certain medications (methotrexate, trimethoprim).
Hypothyroidism — slowed metabolism impairs red cell maturation; TSH screening is part of most macrocytic anaemia work-ups.
Excess alcohol and certain drugs (hydroxyurea, azathioprine) — direct toxic effect on bone marrow proliferation.

WHO 2024 severity classification for adults:

Severity	Haemoglobin
Mild	110–below reference for group
Moderate	80–109 g/L
Severe	below 80 g/L

High haemoglobin

Elevated haemoglobin is less common than anaemia but equally important to investigate.

Secondary erythrocytosis is the body’s response to chronic hypoxia or reduced plasma volume:

COPD, severe asthma, obstructive sleep apnoea — the lungs cannot sustain adequate oxygen saturation, and the body compensates with more red cells.
Prolonged residence at high altitude.
Smoking (as noted above).
Dehydration — “relative” erythrocytosis: the red cell mass is normal but plasma volume is contracted, raising the measured concentration. It resolves with rehydration.

Primary erythrocytosis (polycythaemia vera) is a rare myeloproliferative neoplasm caused by an acquired JAK2 gene mutation. Red cell production is autonomous — independent of erythropoietin stimulation. It carries a meaningful risk of thrombosis and requires haematology assessment. Per the WHO 2022 diagnostic criteria, the haematology work-up threshold is haemoglobin persistently above 165 g/L in men or 160 g/L in women (or haematocrit above 49% / 48%) without an obvious secondary cause.

Haemoglobin vs ferritin — which falls first

This is one of the most practically important patterns in routine haematology. Iron in the body circulates between two compartments: functional iron (incorporated in haemoglobin and myoglobin) and storage iron (bound to ferritin, mainly in the liver, spleen, and bone marrow). In early iron deficiency, the storage compartment is depleted first — ferritin falls while haemoglobin remains within the normal range, sometimes for months or even years.

This is why someone presenting with unexplained fatigue, hair loss, or low mood can receive a “normal” blood count and still have a clinically significant iron deficit. Only when stores are completely exhausted does the bone marrow begin to produce smaller, paler cells, and haemoglobin eventually drops below threshold.

The practical implication: if symptoms are present but haemoglobin is normal, ask your doctor to check ferritin. The two tests are complementary, not interchangeable.

MCV, MCH, and MCHC explained

Every CBC includes three red cell indices that help classify anaemia without waiting for iron studies:

MCV (mean corpuscular volume) — the average size of a red blood cell, measured in femtolitres (fL). Normal range: 80–100 fL. Elevated MCV signals macrocytosis; reduced MCV signals microcytosis.
MCH (mean corpuscular haemoglobin) — the average mass of haemoglobin in a single red cell, measured in picograms. Normal range: 27–34 pg. Reduced MCH (hypochromia) is the hallmark of iron-deficiency anaemia.
MCHC (mean corpuscular haemoglobin concentration) — the ratio of haemoglobin mass to cell volume. Normal range: 320–360 g/L. A raised MCHC is particularly helpful in suspected hereditary spherocytosis.

Together these three indices allow the doctor to classify the anaemia — microcytic hypochromic, normocytic normochromic, or macrocytic — at the initial CBC stage, before any additional investigations come back.

How HealthLab helps you track haemoglobin

A single haemoglobin result is a snapshot. The real clinical value emerges from the trend: is haemoglobin rising in response to iron supplementation? Falling steadily despite adequate diet? Stable over three annual check-ups? A trajectory is the most reliable way to assess treatment response and catch deterioration early.

HealthLab automatically recognises haemoglobin, MCV, MCH, and other blood count parameters from PDF lab reports issued by any laboratory, then builds a time-series chart so you can see how every marker moves from test to test — no manual entry, no spreadsheets.

Download HealthLab on the App Store

Frequently Asked Questions

Can I raise my haemoglobin through diet alone?

For iron-deficiency anaemia, diet is important but rarely sufficient on its own once a true deficiency has developed. Haem iron from animal sources (red meat, liver, fish) is absorbed several times more efficiently than non-haem iron from plant foods; pairing plant iron with vitamin C improves uptake. If anaemia is already diagnosed, supplemental iron is usually prescribed because dietary correction alone takes too long. For other anaemia types — B12 deficiency, macrocytic anaemia — dietary adjustments without treating the underlying cause are generally ineffective.

Should I fast before a CBC test?

Strict fasting is not required for most CBC parameters, including haemoglobin — food does not directly affect red cell indices. However, if the CBC is ordered as part of a broader panel that includes glucose or a lipid profile, follow the preparation instructions for the whole panel, typically an early-morning draw either fasting or after a light meal. Avoid intense exercise in the 24 hours beforehand, as it can transiently affect some white cell and platelet parameters.

Why am I exhausted if my haemoglobin is normal?

A normal haemoglobin does not rule out iron deficiency. Ferritin — the storage form of iron — falls significantly before haemoglobin does, and symptomatic iron depletion (fatigue, hair thinning, poor concentration, reduced cold tolerance) can occur while haemoglobin remains within range. Other common causes of fatigue with a normal CBC include vitamin D deficiency, thyroid dysfunction, and poor sleep. A broader panel — ferritin, TSH, vitamin D — provides a far more complete picture than a blood count alone.

How often should I check my haemoglobin?

For healthy adults with no risk factors, once a year as part of a routine health check — usually within a CBC panel — is sufficient. More frequent testing is appropriate during pregnancy (each trimester and postpartum), when planning pregnancy, for regular blood donors, in chronic gastrointestinal conditions (coeliac disease, inflammatory bowel disease), and after bariatric surgery. If iron supplementation has been started, a repeat CBC at 4–8 weeks allows your doctor to assess the haematological response.

This material does not replace clinical advice. Interpreting laboratory results always requires clinical context.