A hemoglobin test measures the levels of hemoglobin in your blood. Hemoglobin is an iron-rich protein in your red blood cells. It carries oxygen from your lungs to the rest of your body. Your cells need oxygen to grow, reproduce, and make energy for you to function. Your hemoglobin levels provide information about the health of your red blood cells.

A hemoglobin test is a blood test often used to check for anemia, a condition in which your body does not make enough healthy red blood cells. If you have anemia, the cells in your body don't get all the oxygen they need. Hemoglobin levels are usually measured as part of a complete blood count (CBC). A CBC is a group of tests that measure the number and type of cells in your blood.

Source: MedlinePlus, U.S. National Library of Medicine