Hemoglobin (Hgb)
A blood test that measures the amount of hemoglobin, the oxygen-carrying protein in red blood cells, used to evaluate anemia and other blood conditions.
Last medically reviewed: April 10, 2026 | Reviewed by LabResult.MD Editorial Team
What is Hemoglobin?
Hemoglobin is a protein found inside red blood cells that binds to oxygen in the lungs and carries it to tissues throughout the body. It also helps transport carbon dioxide back to the lungs to be exhaled. Hemoglobin gives blood its red color.
Hemoglobin levels are one of the most important indicators of blood health. They are routinely measured as part of a Complete Blood Count (CBC) and are essential for diagnosing anemia, polycythemia, and other conditions that affect the blood's ability to carry oxygen.
Why Is It Tested?
A healthcare provider may order a hemoglobin test to:
- Screen for or diagnose anemia (low red blood cell count)
- Evaluate unexplained fatigue, weakness, or shortness of breath
- Monitor chronic conditions that affect red blood cells (kidney disease, cancer)
- Assess blood loss from surgery, injury, or heavy menstrual periods
- Monitor response to treatment for anemia or other blood disorders
- Evaluate overall health as part of a routine checkup
Normal Reference Ranges
Reference ranges may vary by laboratory, testing method, age, and other factors. Always use the ranges provided on your lab report.
| Population | Normal Range (g/dL) |
|---|---|
| Adult Men | 13.5 – 17.5 g/dL |
| Adult Women | 12.0 – 16.0 g/dL |
| Pregnant Women | 11.0 – 14.0 g/dL |
| Children (1–6 years) | 9.5 – 14.0 g/dL |
| Newborns | 14.0 – 24.0 g/dL |
What Does a High Hemoglobin Level Mean?
Hemoglobin levels above the normal range may indicate that the body is producing too many red blood cells or that other factors are concentrating the blood. High levels could indicate:
- Dehydration (which concentrates red blood cells)
- Polycythemia vera (a bone marrow disorder that overproduces red blood cells)
- Chronic lung disease or heart disease (the body compensates for low oxygen)
- Living at high altitude (the body adapts to less available oxygen)
- Smoking (carbon monoxide from tobacco raises hemoglobin levels)
Consistently high hemoglobin can increase the risk of blood clots. A healthcare provider may recommend further testing to determine the cause.
What Does a Low Hemoglobin Level Mean?
Low hemoglobin is one of the defining features of anemia. Common causes include:
- Iron deficiency (the most common cause of anemia worldwide)
- Vitamin B12 or folate deficiency
- Chronic blood loss (from heavy periods, ulcers, or gastrointestinal bleeding)
- Chronic diseases (kidney disease, cancer, rheumatoid arthritis)
- Bone marrow disorders (aplastic anemia, leukemia)
- Hemolytic anemia (where red blood cells are destroyed faster than they are made)
Symptoms of low hemoglobin may include fatigue, weakness, pale skin, shortness of breath, dizziness, and cold hands or feet. Mild anemia may not cause noticeable symptoms.
Common Next Steps
Depending on the result, a healthcare provider may recommend:
- Iron studies (serum iron, ferritin, TIBC) to evaluate iron-deficiency anemia
- Vitamin B12 and folate levels
- A reticulocyte count to assess how quickly the bone marrow is producing new red blood cells
- A peripheral blood smear to examine red blood cell shape and size
- Additional testing for underlying conditions (kidney function, thyroid function)
- Dietary changes, supplements, or medications depending on the cause
Frequently Asked Questions
What is a normal hemoglobin level?
Normal hemoglobin ranges are 13.5–17.5 g/dL for men and 12.0–16.0 g/dL for women. Levels may vary slightly depending on the laboratory and factors like age, altitude, and pregnancy.
What is the most common cause of low hemoglobin?
Iron deficiency anemia is the most common cause of low hemoglobin worldwide, affecting an estimated 1.2 billion people according to the World Health Organization. Other common causes include vitamin B12 or folate deficiency, chronic disease, and blood loss.
What is the difference between hemoglobin and hematocrit?
Hemoglobin measures the amount of oxygen-carrying protein in red blood cells, while hematocrit measures the percentage of blood volume made up of red blood cells. Both are used to evaluate anemia and are included in a Complete Blood Count (CBC).
Related Tests and Biomarkers
Sources
- World Health Organization. Haemoglobin concentrations for the diagnosis of anaemia (2011)
- MedlinePlus. Hemoglobin Test. U.S. National Library of Medicine
- American Society of Hematology. Anemia Overview
Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice. Reference ranges vary by laboratory. Always discuss your results with a qualified healthcare provider.