Hemoglobin Barts consists of four gamma chains. It is moderately insoluble, and therefore accumulates in the red blood cells. It has an extremely high affinity for oxygen, resulting in almost no oxygen delivery to the tissues. It is produced in the disease alpha-thalassemia and in the most severe of cases, it is the only form of haemoglobin in circulation. In this situation, a fetus will develop hydrops fetalis and normally die before or shortly after birth, unless intrauterine blood transfusion is performed.
Since Hemoglobin Barts is elevated in alpha thalassaemia, it can be measured, providing a useful screening test for this disease in some populations.
The ability to measure hemoglobin Barts makes it useful in newborn screening tests. Newborn babies are tested for many different diseases (varies by country and state) including hemoglobinopathies such as sickle cell disease and thalassemia. If hemoglobin Barts is detected on a newborn screen, the patient is usually referred for further evaluation since detection of hemoglobin Barts can indicate either silent alpha thalassemia carrier (one alpha globin gene deletion), alpha thalassemia trait (two alpha globin gene deletions) or hemoglobin H disease (three alpha globin gene deletions). Deletion of four alpha globin genes in not compatible with life.
This variant of hemoglobin is so called as it was discovered at St. Bartholomew's Hospital in London. The hospital has the fond sobriquet, St. Barts, and the hemoglobin was named hemoglobin Barts.