Hemoglobin (Hb or Hgb) is a protein found in red blood cells that carries oxygen from the lungs to the body's tissues and organs. The hemoglobin test measures the amount of hemoglobin in a person's blood. The normal range for hemoglobin can vary depending on factors such as age, sex, and health status, but generally falls within the following ranges: Men: 13.5 to 17.5 grams per deciliter (g/dL) of blood Women: 12.0 to 15.5 g/dL of blood Children: 11.0 to 16.0 g/dL of blood A low hemoglobin level, called anemia, may indicate conditions such as iron deficiency, vitamin B12 deficiency, folate deficiency, chronic kidney disease, or certain types of cancer. Anemia can also be caused by blood loss due to injury, surgery, or menstruation. Symptoms of anemia may include fatigue, weakness, shortness of breath, and pale skin. A high hemoglobin level, called polycythemia, may indicate conditions such as lung disease, heart disease, or bone marrow disorders. Polycythemia can also be caused by dehydration or living at high altitudes. Symptoms of polycythemia may include headaches, dizziness, and difficulty breathing.