Hemoglobin measures the amount of oxygen-carrying protein in your red blood cells. Typical reference ranges are about 13.5–17.5 g/dL for men and 12.0–15.5 g/dL for nonpregnant women, though ranges vary slightly by lab. It is the core marker used to assess whether your blood is carrying oxygen efficiently.

Low hemoglobin suggests anemia, which can result from iron deficiency, B12 or folate deficiency, blood loss, chronic disease, hemolysis, or bone marrow disorders. High hemoglobin can reflect dehydration, chronic low-oxygen states, or less commonly disorders such as polycythemia.