Hemoglobin is the oxygen-carrying protein in red blood cells. Measured in a CBC, hemoglobin levels help detect anemia or polycythemia, guide treatment (iron, B12/folate, disease-specific therapy), and inform transfusion decisions. Typical adult ranges are ~13.8-17.2 g/dL for men and 12.1-15.1 g/dL for women; WHO defines anemia as <13 g/dL in men and <12 g/dL in non-pregnant women.
What hemoglobin is
Hemoglobin is the iron-containing protein inside red blood cells that carries oxygen from the lungs to tissues and returns a portion of carbon dioxide to the lungs. A hemoglobin molecule is a tetramer made of four globin chains, each bound to a heme group that contains iron. Healthy hemoglobin levels keep tissues supplied with oxygen and support normal cellular function.Why clinicians measure hemoglobin
A hemoglobin test is usually part of a complete blood count (CBC). Clinicians use it to:- Detect anemia (low hemoglobin) or polycythemia (high hemoglobin).
- Monitor response to treatments such as iron therapy, vitamin B12/folate replacement, or erythropoiesis-stimulating agents.
- Help decide whether a blood transfusion is needed in cases of severe or symptomatic anemia.
What the numbers mean
Reference ranges vary by laboratory. Typical adult ranges are about 13.8-17.2 g/dL for men and 12.1-15.1 g/dL for women. The World Health Organization defines anemia as hemoglobin below 13 g/dL in men and below 12 g/dL in non-pregnant women. Doctors interpret results in the context of symptoms, medical history, and other CBC indices.Common causes of abnormal hemoglobin
Low hemoglobin (anemia) can result from:- Iron deficiency (common worldwide)
- Chronic disease and inflammation
- Vitamin B12 or folate deficiency
- Acute or chronic blood loss
- Hemolysis (accelerated red cell destruction)
- Dehydration (relative increase)
- Smoking or living at high altitude
- Chronic lung disease that lowers oxygen levels
- Myeloproliferative disorders such as polycythemia vera
Potential complications and treatment principles
Severe, untreated anemia forces the heart to pump harder to meet oxygen demands, which can cause rapid heartbeat and long-term strain on the heart. Treatment targets the underlying cause: iron supplements and dietary changes for iron deficiency, B12 or folate for deficiency states, bleeding control, or disease-specific therapy for marrow disorders. Transfusions are reserved for severe or symptomatic cases; many guidelines use thresholds around 7-8 g/dL for stable hospitalized patients, but clinicians individualize decisions based on symptoms and comorbidities.When to see a clinician
See a clinician if you have symptoms such as persistent fatigue, shortness of breath, dizziness, palpitations, or signs of bleeding. A simple CBC including hemoglobin is the usual first step toward diagnosis and treatment.FAQs about Hemoglobin Blood Tests
What is a normal hemoglobin level?
Normal ranges vary by laboratory. Typical adult values are about 13.8-17.2 g/dL for men and 12.1-15.1 g/dL for women. The World Health Organization defines anemia as hemoglobin below 13 g/dL in men and below 12 g/dL in non-pregnant women.
What causes low hemoglobin (anemia)?
Common causes include iron deficiency, chronic disease or inflammation, vitamin B12 or folate deficiency, blood loss, and hemolysis. The treatment depends on the specific cause.
When is a blood transfusion recommended for low hemoglobin?
Transfusion is generally reserved for severe or symptomatic anemia. Many modern guidelines use thresholds around 7-8 g/dL for stable hospitalized patients, but clinicians consider symptoms, ongoing bleeding, and comorbidities when deciding.
Can dehydration affect hemoglobin readings?
Yes. Dehydration reduces plasma volume and can raise hemoglobin concentration temporarily (a relative increase). Clinicians consider hydration status when interpreting results.
How is hemoglobin tested?
Hemoglobin is measured from a blood sample obtained by venipuncture or fingerstick and reported in grams per deciliter (g/dL) as part of a CBC.