Glossary of Sickle Cell Disease Terms

Reviewed by: HU Medical Review Board | Last reviewed: January 2021


Acute chest syndrome

Condition characterized by chest pain, cough, fever, and difficulty breathing. ACS is a potentially life-threatening complication of SCD and requires transfusions and intensive care hospitalization.1


Condition where you have a lower than normal number of healthy red blood cells. It is a common complication of SCD and can cause tiredness, dizziness, difficulty breathing, jaundice, and slow growth.2



Someone who has the gene for a disease but does not show symptoms of the disease. People who have only 1 abnormal hemoglobin gene have sickle trait and are “carriers” of the sickle cell gene.3



Painful swelling of the hands and feet caused by blocked blood flow in small bones. It is most common in children and is one of the first symptoms of sickle cell disease.4


Exchange Transfusion

A type of blood transfusion where some of your blood is replaced by a blood from a donor who has healthy red blood cells. This decreases the risk for iron overload.1



Common problem in sickle diseases where pieces of solid material form in the gallbladder.1


Sequence of DNA that provides instructions for the body to make a protein. One copy of each gene is passed down from each parent to a child. For example, the HBB gene provides instructions for the body to make a subunit of the protein hemoglobin.1

Genetic counselor

Healthcare provider who has special training in inherited conditions. They can interpret genetic testing and provide risk assessment, education, and support to families having children at risk for sickle cell disease.5



Doctor who has special training in blood disorders. They are often the doctors managing the long-term care of people with sickle cell disease.6


The protein in red blood cells that carries oxygen from the lungs to other parts of the body. The specific type of hemoglobin depends on which types of smaller units assemble together.7

Hemoglobin A

The most common type of normal hemoglobin in adults. It is made up of 4 smaller proteins: 2 alpha globin units and 2 beta globin units. Beta globin is mutated in people with sickle cell disease.1

Hemoglobin F (fetal hemoglobin)

The normal hemoglobin found in newborn infants. Fetal hemoglobin protects red blood cells from sickling. It decreases in quantity during the first year of life and infants begin to show symptoms.1

Hemoglobin S (sickle hemoglobin)

Abnormal hemoglobin present in all people with sickle cell disease. In hemoglobin S, the beta globin subunit has a single mutation that causes it to clump together inside red blood cells.1


Medicine that reduces complications of sickle cell disease. It works by increasing the amount of hemoglobin F.8



To receive a certain trait from a parent through genes. People with sickle cell disease inherit 2 abnormal hemoglobin genes from their parents.8



Yellowing of the skin and eyes. It happens when many red blood cells burst quickly.2



Severe disease caused by infection with a parasite transmitted by mosquitoes. Sickle cell trait provides protection against severe malaria, which is why the sickle hemoglobin gene is common in areas affected by malaria.1


Alteration in the sequence of a gene. In sickle cell disease, the HBB gene has a single mutation that causes the beta globin unit of hemoglobin to also have a mutation.1


Pain crisis (also known as sickle crisis or vaso-occlusive crisis)

Pain due to blocked blood vessels by sickled blood cells. Pain most often occurs in the arms, legs, back, and abdomen. It is the most common cause of hospitalization for people with sickle cell disease.2


Prolonged painful erection of the penis. It occurs when blood flow out of the penis is blocked by sickled cells.2


Recessive trait

A trait that shows up only when an organism has 2 copies of the abnormal gene. Sickle cell disease is an example of a recessive trait.7

Red blood cell

A type of blood cell containing hemoglobin that carries oxygen throughout the body. Healthy red blood cells are round and flexible so they can squeeze through small blood vessels.8



A c-shaped farm tool. Red blood cells in people with sickle cell disease are shaped like sickles.8

Sickle cell anemia (HbSS)

Most common and severe type of sickle cell disease. It occurs when someone inherits 2 genes for hemoglobin S.8

Sickle cell disease

Group of inherited red blood cell disorders. People with sickle cell disease have an abnormal form of hemoglobin that causes red blood cells to become rigid and sickle-shaped. These sickle cells block blood flow and burst prematurely.8

Sickle cell trait

Inheritance of 1 gene for normal hemoglobin A and 1 gene for hemoglobin S. People who have sickle cell trait do not show symptoms of sickle cell disease.3

Splenic sequestration

Condition where red blood cells get trapped in the spleen, making it too large. It can lead to severe anemia.2



Group of inherited red blood cell disorders. It happens when a mutation in a hemoglobin gene reduces the amount of hemoglobin.7


Process of giving someone blood with normal red blood cells. Blood transfusions are often done to treat acute chest crises or prevent complications.2


Operation in which an organ or tissue is replaced. The only cure for sickle cell disease is a bone marrow transplant, but it is rarely done.8


Unusual hemoglobin

Any hemoglobin besides hemoglobin A or F, such as hemoglobin S, C, E, or D.1

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