What is hemoglobin S?
Hemoglobin is the part of red blood cells that carries oxygen to all parts of the body. The usual type of hemoglobin is called hemoglobin A. Genes that we inherit from each of our parents determine what type of hemoglobin we have. Hemoglobin S is a hemoglobin protein that is different from the common Hemoglobin A, and shows up separately on special testing.
There are different forms of sickle cell disease depending on the hemoglobin genes inherited:
- Sickle cell anemia, which includes sickle cell disease type SS and type sickle beta zero(Sβ0) thalassemia
- Sickle cell disease type SC
- Sickle cell disease type sickle beta plus (Sβ+) thalassemia
- Sickle cell disease type SD, SE, and other sickle cell disease variants
What is sickle cell disease?
Sickle cell disease is an inherited blood disease that causes problems with red blood cells. Red blood cells circulate in the blood and contain hemoglobin, which carries oxygen to all parts of the body, and normal red blood cells are shaped like a disc. In sickle cell disease, the abnormal hemoglobin (hemoglobin S) sticks together in low oxygen situations deep in the body, causing the red cells to assume a curved shape like a sickle (a farming curved cutting tool, daranti). Sickle cells are less flexible and block the flow of in blood vessels causing problems
What are the signs and symptoms of sickle cell?
Symptoms of sickle cell disease can vary, and a few patients may have only mild anemia and intermittent problems. However, many will have anemia sufficient to cause tiredness. In addition when sickle cells block blood vessels this can lead to:
- Pain crisis: pain in the chest, stomach, or bones
- Acute chest syndrome: shortness of breath which can be life threatening
- Stroke: weakness of one half of the body which can be permanent
- Kidney damage: which can eventually lead to kidney failure
- Retinal damage: which can eventually lead to vision loss
- Destruction of the spleen: which makes patients more prone to certain kinds of infection(e.g. pneumococcal)
Infection, fever and stress can cause destruction of more red blood cells than usual, causing the hemoglobin level to drop further and with jaundice of the skin and whites of the eyes. Since red blood cells are produced in the bone marrow, sometimes a viral infection (e.g. parvovirus) can cause the bone marrow to stop cell production temporarily causing a drop in hemoglobin with lack of reticulocytes in the blood. This is called an “aplastic crisis” and may last for several days before red blood cell production will resume, during which anemia may be severe enough to require a red blood cell transfusion.
How is sickle cell diagnosed?
The history and physical findings, and anemia with sickle cells in the peripheral blood smear suggest the diagnosis. Often the first indication is an acute crisis e.g. splenic sequestration crisis where blood is trapped in the spleen with a sudden anemia. Confirmatory tests are:
Sickle cell test: in which a patient’s red blood cells are placed in a special solution and undergo sickling (SickleDex). Unfortunately this is a screening test and less reliable.
Hemoglobin electrophoresis test: in which the patient’s red cells are subjected to an electric field and hemoglobin S shows up differently from hemoglobin A. This test is confirmatory.