Hemoglobin is the substance in red blood cells that contains iron and transports oxygen from the lungs to the rest of the body. It also transports gases such as carbon dioxide and nitric oxide. Hemoglobin assists in removing carbon dioxide from the bloodstream through the lungs during exhalation. Nitric oxide is essential for transporting oxygen to tissues, as well as maintaining unimpeded blood flow. Hemoglobin plays a significant role in facilitating the flow of nitric oxide to all areas of the body. Other cells besides red blood cells contain hemoglobin, including dopaminergic neurons in the brain, the eye’s retinal pigment, and cervical cells. In these tissues, hemoglobin regulates iron metabolism and also serves as an antioxidant rather than an oxygen transporter.

1. Variants of Hemoglobin (Hemoglobinopathies)

Abnormal hemoglobin conditions are almost always present at birth. Some hemoglobin variants do not cause illness while other produce pathological symptoms. The most well-known hemoglobinopathy is sickle-cell anemia or Hemoglobin S, but individuals may also be born with

  • Hemoglobin H — found in varieties of thalassemia, a disease causing severe anemia
  • Hemoglobin E — causes chronic hemolytic anemia
  • Hemoglobin Barts — present in types of thalassemia
  • Hemoglobin C — sometimes found in cases of hemolytic anemia
  • Hemoglobin Hopkins-2 — a hemoglobin abnormality causing sickle cell disease when combined with hemoglobin S

Hemoglobin assists ironBlackJack3D / Getty Images