hemoglobin (Hb, Hgb) test, a blood test that measures the total amount of hemoglobin in the peripheral blood, which reflects the number of red blood cells in the blood. The test is normally performed as part of a complete blood count.Abnormal levels indicate anemia, erythrocytosis, and sickle cell disease, among others. 1  Facebook. blood test that measures the total amount of hemoglobin in the peripheral blood, which reflects the number of red blood cells in the blood. The test is normally performed as part of a complete blood count.