concentration of oxygen-carrying protein in red blood cells
Hemoglobin levels, often abbreviated as Hb levels, refer to the concentration of hemoglobin in the blood. Hemoglobin is a protein in red blood cells responsible for transporting oxygen from the lungs to the rest of the body and returning carbon dioxide from the tissues back to the lungs. Normal hemoglobin levels vary by age and sex, and deviations from the norm can indicate conditions such as anemia or polycythemia.