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Hemoglobin

Complete Blood Count

HbHemoglobin concentration

Review status

Currently under review

Pending specialist review and validation.

What it shows

Hemoglobin is the iron-containing protein inside your red blood cells that carries oxygen from your lungs to the rest of your body and helps return carbon dioxide to your lungs to be exhaled. A hemoglobin test measures the amount of this protein in your blood.

It is most often part of a complete blood count, a common panel that also includes other red blood cell measurements. Your sample is usually taken from a vein in your arm, and the result helps your clinician understand how well your blood is delivering oxygen.

Why it matters

Hemoglobin levels help identify conditions like anemia, which can cause fatigue, shortness of breath, pale skin, headaches, and reduced exercise tolerance. Low levels can result from iron deficiency, blood loss, chronic kidney disease, vitamin B12 or folate deficiency, inflammation, or red blood cell destruction.

Higher-than-usual levels may occur with dehydration, living at high altitude, smoking, lung or heart disease, sleep apnea, or certain bone marrow conditions. Clinicians use hemoglobin to evaluate symptoms, monitor chronic illnesses, assess recovery after bleeding or surgery, and track response to treatments such as iron therapy or medications that stimulate red blood cell production.

Understanding your results

Your result is interpreted using a reference range appropriate for your age and sex, your symptoms, and other blood indices. A single value is less informative than trends over time, so your clinician may compare it with prior results and related tests like hematocrit, mean cell volume, mean cell hemoglobin, and reticulocyte count.

If your hemoglobin is lower than expected, your clinician may look for causes such as iron deficiency, vitamin B12 or folate deficiency, chronic kidney disease, inflammation, or blood loss from the gastrointestinal or gynecologic tract. If it is higher than expected, they may consider dehydration, smoking, high-altitude residence, lung or heart conditions, sleep apnea, or rare bone marrow disorders. Follow-up can include additional blood tests, nutrition review, and, when indicated, imaging or procedures. Do not start supplements like iron without guidance, since the right treatment depends on the cause.

Reference ranges

135 – 195 g/L
Female
0 days – 2 days
135 – 195 g/L
Male
0 days – 2 days
135 – 185 g/L
Female
2 days – 8 days
135 – 185 g/L
Male
2 days – 8 days
135 – 180 g/L
Female
8 days – 14 days
135 – 180 g/L
Male
8 days – 14 days
135 – 180 g/L
Female
14 days – 1 month
135 – 180 g/L
Male
14 days – 1 month
95 – 135 g/L
Female
1 month – 6 months
95 – 135 g/L
Male
1 month – 6 months
105 – 135 g/L
Female
6 months – 2 years
105 – 135 g/L
Male
6 months – 2 years
115 – 135 g/L
Female
2 years – 6 years
115 – 135 g/L
Male
2 years – 6 years
115 – 155 g/L
Female
6 years – 16 years
115 – 155 g/L
Male
6 years – 16 years
120 – 160 g/L
Female
16 years – 150 years
135 – 175 g/L
Male
16 years – 150 years

Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.

Factors that could impact Hemoglobin

  • Hydration status

    Dehydration concentrates your blood and can make hemoglobin appear higher, while overhydration can dilute it and make the value appear lower. Repeating the test after correcting fluids can clarify results.

  • Altitude and smoking

    Living at high altitude or smoking can increase hemoglobin as your body adapts to lower oxygen levels. Quitting smoking and allowing time after relocation can change results.

  • Pregnancy

    During pregnancy, plasma volume expands more than red cell mass, which can lower measured hemoglobin. Your clinician interprets results in the context of pregnancy stage and overall health.

  • Menstrual and other blood loss

    Heavy periods, recent surgery, injury, or hidden gastrointestinal bleeding can reduce hemoglobin. Your clinician may ask about symptoms like dark stools, fatigue, or dizziness.

  • Chronic kidney disease

    Kidneys produce erythropoietin, a hormone that signals the bone marrow to make red blood cells. Reduced production in kidney disease can lower hemoglobin levels over time.

  • Nutritional status and supplements

    Low iron, vitamin B12, or folate can lower hemoglobin, while appropriate supplementation can raise it. Taking iron when it is not needed can be harmful, so testing guides the plan.

  • Medications and therapies

    Erythropoiesis-stimulating agents, chemotherapy, certain antibiotics, and antiretroviral drugs can affect hemoglobin. Recent blood transfusions can temporarily change results.

  • Sample quality and timing

    Hemolysis, clotting, or delays in processing can affect some red blood cell indices and may prompt a repeat sample. Illness, recent exercise, or acute stress can also influence measurements.

2026

References

  1. McGill University Health Centre. (2016, December 14). Hemoglobin (Task CD 316660). Laboratory reference ranges.
  2. World Health Organization. (2011). Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity.
  3. Kidney Disease: Improving Global Outcomes (KDIGO) Anemia Work Group. (2012). KDIGO clinical practice guideline for anemia in chronic kidney disease. Kidney International Supplements, 2(4), 279-335.