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Blood health

Hemoglobin

Also known as: Hemoglobin concentration test, Hb test, Hgb test, Part of a complete blood count (CBC)

Hemoglobin (Hb) is an iron-containing protein in red blood cells. It binds with oxygen in the lungs and releases it into the tissues. It also helps carry carbon dioxide back to the lungs so you can breathe it out. 

A hemoglobin test measures the amount of Hb in a given volume of blood, reflecting the blood’s capacity to transport oxygen.

Hemoglobin levels can go up or down if your body makes fewer red blood cells, if red blood cells break down too quickly, or if you lose blood. Changes in hemoglobin can be an early sign of conditions like anemia (too little hemoglobin), polycythemia (too much hemoglobin), or inherited blood disorders such as sickle cell disease or thalassemia. 

Doctors almost always look at hemoglobin as part of a complete blood count (CBC), along with other measures like hematocrit and red blood cell size and number. 

From a telehealth or virtual care standpoint, providers can order hemoglobin (and CBC) testing remotely, review results, and recommend further workup or interventions without requiring an initial in-person visit. Abnormal results may prompt referrals for specialized hematology evaluation or in-person diagnostics when needed.

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Key takeaways

  • Sample required: Venous blood draw is standard for hemoglobin testing (sometimes, a finger-stick sample may be used in point-of-care settings, like a hospital bed).

  • Tests for: The concentration of hemoglobin in blood. This oxygen-carrying protein in red blood cells is a core marker of anemia, polycythemia, and general red cell health.

  • Healthy/Normal ranges: Approximately 12.0–15.5 g/dL in women (lab- and population-specific).

What can a hemoglobin test tell you?

A hemoglobin test doesn’t diagnose a specific condition on its own. Instead, it helps healthcare providers evaluate for conditions that affect red blood cells or oxygen transport, including:

  • Anemia. Low hemoglobin suggests that your body isn’t carrying enough oxygen, which can cause fatigue, shortness of breath, or dizziness.

  • Polycythemia. High hemoglobin levels may indicate that your body is making too many red blood cells, often due to chronic low oxygen (from lung disease or high altitude) or a bone marrow disorder.

  • Inherited blood disorders. Abnormal hemoglobin results can prompt testing for sickle cell disease or thalassemia, which change the shape or function of red blood cells.

  • Monitoring treatment. Providers may check hemoglobin to track progress in people taking iron, vitamin B12, or folate supplements, or those receiving treatment for chronic illnesses that affect blood production.

What is being tested?

Hemoglobin levels show how much oxygen-carrying protein your red blood cells contain.

  • Normal function. Hemoglobin picks up oxygen in your lungs and delivers it to your body’s tissues. It also transports carbon dioxide back to the lungs for exhalation.

  • Fluctuations. Levels can rise or fall depending on how many red blood cells your body makes, how quickly they break down, or how much blood you lose.

  • Clinical relevance. Changes in hemoglobin may be an early clue to anemia (low Hb), polycythemia (high Hb), or inherited conditions that affect hemoglobin structure.

Doctors almost always interpret hemoglobin as part of a complete blood count (CBC).  Altitude, smoking, and other environmental factors can influence Hb concentration and must sometimes be corrected for in interpretation (e.g., altitude adjustment per WHO guidance).

Where is the hemoglobin typically included?

Hemoglobin is rarely ordered in isolation. It is a core component of the complete blood count (CBC), which also measures:

  • Hematocrit (percentage of blood volume occupied by red cells).

  • Red blood cell (RBC) count.

  • RBC indices, which help evaluate the size, hemoglobin content, and concentration of red blood cells  (MCV, MCH, MCHC).

  • White blood cells, platelets, and related differential counts.

Additionally, a CBC, which is commonly ordered for:

  • Routine health checkups.

  • Preoperative labs.

  • Symptom-driven investigations (e.g., fatigue, pallor).

  • Chronic disease monitoring (e.g., kidney disease, bone marrow disorders).

Who should get a hemoglobin test?

While there is no universal guideline recommending hemoglobin testing in all adults, it is commonly recommended if you:

  • Have symptoms suggestive of anemia, including fatigue, pallor, shortness of breath, dizziness, or palpitations.

  • Have risk factors for blood loss or deficiency, including menstrual bleeding, GI bleeding, surgery, or trauma.

  • Have chronic medical conditions, including kidney disease, inflammatory diseases, cancer, or bone marrow disorders.

  • Are part of a high-risk group. This includes infants/young children with risk factors, pregnant individuals (ACOG recommends screening early and again at 24–28 weeks), and some older adults—based on clinician judgment.

  • Are found to have an abnormally high number of red blood cells. This can suggest polycythemia or erythrocytosis. This can occur in people who live at high altitudes or have chronic lung disease, as the body produces more red cells to compensate for lower oxygen levels.

  • Baseline and monitoring in therapy: e.g., monitoring the body’s response to iron therapy, B12/folate therapy, or medications that stimulate the body’s production of red blood cells (erythropoiesis-stimulating agents or ESAs).

Telehealth providers can help assess whether a hemoglobin test is warranted based on symptoms, history, and virtual examination, and arrange for lab orders.

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Not available in all 50 states. Eligibility and provider order required. Lab results alone are not intended to diagnose, treat, or cure any condition. A provider will reach out about critical results and plans include access to 24/7 provider messaging.

Images for illustrative purposes only.

Frequently asked questions

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What causes changes in hemoglobin levels?

Many factors influence hemoglobin levels, which is why your results should always be interpreted by a healthcare provider who can consider your overall health, symptoms, and other lab findings before making any conclusions.

Increased levels can result from living at high altitude, smoking, or dehydration (as less plasma volume makes hemoglobin appear higher). Additionally, chronic lung disease or low oxygen states, and bone marrow disorders (like polycythemia vera) can cause increased hemoglobin levels

Decreased levels can result from iron deficiency resulting from diet, or heavy bleeding (from injury, menstruation, or ulcers). Chronic illness (particularly kidney or liver disease), vitamin B12 or folate deficiency, bone marrow suppression (from chemotherapy or certain medications), and inherited disorders like sickle cell disease or thalassemia can also lead to decreased levels. 

What are normal hemoglobin levels?

Normal ranges of hemoglobin are approximately 12.0 to 15.5 g/dL grams per deciliter (g/dL) in women  (lab- and population-specific).

Can I do a hemoglobin test at home?

Some at-home kits (finger-stick) exist, but lab-based venous tests are more accurate and preferred for diagnosis.

Do I need to fast before a hemoglobin test?

No. Hemoglobin measurement itself doesn’t require fasting, though other tests in the same panel might.

Does insurance typically cover a hemoglobin test?

Yes, when medically necessary (e.g., symptoms, chronic illness, or part of a complete blood count [CBC]). Insurance is not required with lab testing through Hers. 

How long until I get results for my hemoglobin test?

Most laboratories return CBC/Hb results within 24 hours.

Can high altitude affect my Hb?

Yes — living at a higher altitude increases baseline Hb; adjustments may be needed using WHO guidelines.

Why are WHO cutoffs under debate?

Some studies suggest that WHO anemia cutoffs may be set a little high (above the fifth percentile in healthy populations), raising the possibility of overdiagnosis in certain settings.

What tests are related to this biomarker?

• Complete Blood Count (CBC). Hemoglobin is a core CBC component.

• Iron Studies. Ferritin, serum iron, TIBC, and transferrin saturation.

• Vitamin B12 / Folic Acid. To evaluate macrocytic (large cell) anemias.

• Hemoglobin Electrophoresis. For suspected hemoglobinopathies (e.g., sickle cell disease, thalassemia).

• Reticulocyte Count. Indicates bone marrow response to anemia.

• Bone Marrow Biopsy / JAK2 Testing. In suspected primary hematologic disorders (e.g, polycythemia vera).

The information provided here is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always talk to a qualified healthcare provider about your specific health concerns.

Related biomarkers

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Hematocrit

Hematocrit is a test that measures the percentage of your blood that is made up of red blood cells, which carry oxygen throughout your body. Being in the healthy range means your blood cells are successfully transporting oxygen to your tissues to sustain bodily functions.

Learn more about Hematocrit

Mean Corpuscular Hemoglobin Concentration (MCHC)

Mean corpuscular hemoglobin concentration (MCHC) measures the average concentration of hemoglobin in your red blood cells, which reflects how effectively they carry oxygen. When MCHC is in the healthy range, it indicates that the body is likely not experiencing any red blood cell disorders or iron deficiency.

Learn more about Mean Corpuscular Hemoglobin Concentration (MCHC)

Mean Corpuscular Hemoglobin (MCH)

Mean corpuscular hemoglobin (MCH) measures the average amount of hemoglobin in each red blood cell, which shows how well your blood can carry oxygen. A healthy level means your blood has enough hemoglobin for proper oxygen transport.

Learn more about Mean Corpuscular Hemoglobin (MCH)

Mean Corpuscular Volume (MCV)

Mean corpuscular volume (MCV) measures the average volume of your red blood cells, which can help reveal early signs of nutrient deficiencies or other blood conditions.

Learn more about Mean Corpuscular Volume (MCV)

Mean Platelet Volume (MPV)

Mean platelet volume (MPV) measures the average volume of your blood platelets, which play an essential role in blood clotting. When your MPV is in the healthy range, it suggests that your platelet volume is normal.

Learn more about Mean Platelet Volume (MPV)

Platelet Count

Platelets are the blood cells that help your body form clots, stopping bleeding when needed. A healthy platelet count means your body generally supports normal blood clotting when necessary.

Learn more about Platelet Count

Red Blood Cell Count

Red blood cells are responsible for carrying oxygen throughout your body. Your healthy red blood cell count is helping your organs and tissues function at their best.

Learn more about Red Blood Cell Count

Red Cell Distribution Width (RDW)

Red cell distribution width (RDW) measures the variation in the size of your red blood cells, which can help detect early signs of anemia or other blood conditions. A healthy RDW suggests that your red blood cells are uniform and efficiently transporting oxygen throughout your body.

Learn more about Red Cell Distribution Width (RDW)

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Reviewed by Felix Gussone, MD

Published 12/04/2025