What Are Hemoglobin Levels?

Hemoglobin levels refer to the concentration of hemoglobin in the blood. Hemoglobin is a protein in red blood cells responsible for carrying oxygen from the lungs to the rest of the body and returning carbon dioxide from the body to the lungs to be exhaled. Hemoglobin levels are measured through a blood test and are expressed in grams per deciliter (g/dL).