Alternative names
Anemia - sickle cell; Hemoglobin SS disease (Hb SS); Sickle cell disease

Definition
Sickle cell anemia is an inherited disease in which the red blood cells, normally disc-shaped, become crescent shaped. As a result, they function abnormally and cause small blood clots. These clots give rise to recurrent painful episodes called “sickle cell pain crises.”

Causes, incidence, and risk factors

Sickle cell anemia is caused by an abnormal type of hemoglobin (oxygen carrying molecule) called hemoglobin S. It is inherited as an autosomal recessive trait - that is, it occurs in someone who has inherited hemoglobin S from both parents.

Someone who inherits hemoglobin S from one parent and normal hemoglobin (A) from the other parent will have sickle cell trait. Approximately 8% of African Americans have sickle cell trait. Someone who inherits hemoglobin S from one parent and another type of abnormal hemoglobin from the other parent will have another form of sickle cell disease, such as sickle cell-b 0 thalassemia, hemoglobin SC disease, or sickle cell-b + thalassemia. Someone with sickle cell trait or these forms of sickle cell disease will usually have no symptoms or only mild ones. However, some of these conditions can cause symptoms similar to sickle cell anemia.

Sickle cell disease is much more common in certain ethnic groups, affecting approximately one out of every 500 African Americans. Because people with sickle trait were more likely to survive malaria outbreaks in Africa than those with normal hemoglobin, it is believed that this genetically aberrant hemoglobin evolved as a protection against malaria.

Although sickle cell disease is inherited and present at birth, symptoms usually don’t occur until after 4 months of age. Sickle cell anemia may become life-threatening when damaged red blood cells break down (hemolytic crisis), when the spleen enlarges and traps the blood cells (splenic sequestration crisis), or when a certain type of infection causes the bone marrow to stop producing red blood cells (aplastic crisis). Repeated crises can cause damage to the kidneys, lungs, bones, eyes, and central nervous system.

Blocked blood vessels and damaged organs can cause acute painful episodes. These painful crises, which occur in almost all patients at some point in their lives, can last hours to days, affecting the bones of the back, the long bones, and the chest. Some patients have one episode every few years, while others have many episodes per year. The crises can be severe enough to require admission to the hospital for pain control and intravenous fluids.

Many manifestations of this disease are a result of the fragility and inflexibility of the sickle red blood cells. When patients experience dehydration, infection, and low oxygen supply, these fragile red blood cells assume a crescent shape, causing red blood cell destruction and poor flow of these blood cells through blood vessels, resulting in a lack of oxygen to the body’s tissues.

Symptoms

 
• joint pain and other bone pain  
• fatigue  
• breathlessness  
• rapid heart rate  
• delayed growth and puberty  
• susceptibility to infections  
• ulcers on the lower legs (in adolescents and adults)  
• jaundice  
• bone pain  
• attacks of abdominal pain  
• fever

Additional symptoms that may be associated with this disease:

 
• bloody urine (hematuria)  
• excessive urination, excessive volume  
• thirst, excessive  
• unwanted painful erection (priapism; this occurs in 10-40% of men with the disease)  
• chest pain  
• poor eyesight/blindness

Signs and tests

Common signs include:

 
• paleness  
• yellow eyes/skin  
• growth retardation

Tests commonly performed to diagnose and monitor patients with sickle cell anemia include:

 
• Complete blood count (CBC)  
• Hemoglobin electrophoresis  
• Sickle cell test

Patients with sickle cell may have abnormal results on certain tests, as follows:

 
• peripheral smear displaying sickle cells  
• urinary casts or blood in the urine  
• Hemoglobin; serum decreased  
• elevated bilirubin  
• high white blood cell count  
• elevated serum potassium  
• elevated serum creatinine  
• blood oxygen saturation may be decreased  
• CT scan or MRI can display strokes in certain circumstances

Treatment

Patients with sickle cell disease need certain treatment and follow-up even when not having a painful crisis. Supplementation with folic acid, an essential element in producing cells, is required because of the rapid red blood cell turnover.

Bacterial infections in children are common and antibiotics and vaccines are given to prevent this complication. Eye examinations by an ophthalmologist are important because of the risk of damage to the retina.

Treatment for sickle cell disease usually focuses on symptoms. While bone marrow transplant can be curative, this therapy is indicated in only a minority of patients, predominantly because of the high risk of the procedure and difficulty in finding suitable donors. Therefore, the purpose of therapy is to manage and control symptoms resulting from crises and to try to limit the frequency of crises.

During a sickle crisis, certain therapies may be necessary. Painful episodes are treated with analgesics and adequate liquid intake. Treatment of pain with adequate analgesics is critical. Non-narcotic medications may be effective, but some patients will require narcotics. Despite common belief to the contrary, narcotic addiction is not more frequent in patients with sickle cell disease than in other chronic pain patients.

Additional treatments include: antibiotics for infection; partial exchange transfusion for acute chest syndrome; potentially partial exchange transfusions or surgery for neurological events, such as strokes, dialysis, or kidney transplant for kidney disease, irrigation or surgery for priapism, surgery for eye problems; hip replacement for avascular necrosis of the hip (death of the joint); gallbladder removal (if there is significant gallstone disease); wound care, zinc oxide, or surgery for leg ulcers; drug rehabilitation and counseling for the psychosocial complications.

Hydroxyurea (Hydrea) was found to help some patients by reducing the frequency of painful crises and episodes of acute chest syndrome and decreasing the need for blood transfusions. There has been some concern about the possibility of this drug causing leukemia, but as yet there are no definitive data that Hydrea causes leukemia in sickle cell patients.

Newer drugs are being developed to manage sickle cell anemia. Some of these agents work by trying to induce the body to produce more fetal hemoglobin (therefore decreasing the amount of sickling) or by increasing the binding of oxygen to sickle cells. But as yet, there are no other widely used drugs that are available for treatment.

Bone marrow transplants are currently the only potential cure for sickle cell anemia. In this treatment the patient’s bone marrow (which makes the sickled red blood cells) is replaced with bone marrow from another individual without sickle cell disease. However, it is difficult to find the right bone marrow donor, and the drugs needed to make the transplant possible are highly toxic. Also, bone marrow transplants are much more expensive than other treatments. Gene therapy (replacing the Hemoglobin S with a normal Hemoglobin A) may be the ideal treatment, but it has proven to be very difficult in humans.

Parents whose children have sickle cell should encourage their children to lead normal lives. However, in order to decrease the occurrence of sickle cell crises, consider the following precautions:

To prevent tissue deoxygenation, avoid the following:

  1. Strenuous physical activity, especially if the spleen is enlarged
  2. Emotional stress
  3. Environments with low oxygen content (high altitudes, non-pressurized airplane flights)
  4. Known sources of infection

To promote proper hydration:

  1. Recognize signs of dehydration
  2. Avoid excess exposure to the sun
  3. Provide access to fluids, both at home and away

To avoid sources of infection:

  1. Keep child properly immunized as recommended by the health care provider
  2. Consider having the child wear a Medic Alert Bracelet
  3. Share above information with teachers and other caretakers as appropriate
  4. Be aware of the effects that chronic, life-threatening illnesses can have on siblings, marital relationships, parents, and the child

Support Groups

Sickle cell anemia, like other chronic, life-threatening diseases, can cause great stress to the patient and family members. Joining a support group, where members share common experiences and problems, can relieve this stress. See sickle cell anemia - support group.

Expectations (prognosis)

In the past, death from organ failure often occurred between the ages of 20 and 40 in most sickle-cell patients. More recently, because of better understanding and management of the disease, patients live into their forties and fifties.

Causes of death include organ failure and infection. Some people with the disease experience minor, brief, and infrequent episodes. Others experience severe, prolonged, and frequent episodes resulting in many complications.

Complications

 
• recurrent aplastic and hemolytic crises resulting in anemia and gallstones  
• multisystem disease (kidney, liver, lung)  
• narcotic abuse  
• splenic sequestration syndrome  
• acute chest syndrome  
• erectile dysfunction (as a result of priapism)  
• blindness/visual impairment  
• neurologic symptoms and stroke  
• joint destruction  
• gallstones  
• infection, including pneumonia, cholecystitis (gallbladder), osteomyelitis (bone), and urinary tract infection  
• parvovirus B19 infection resulting in aplastic crisis  
• tissue death of the kidney  
• loss of function of the spleen  
• leg ulcers  
• death

Calling your health care provider

Call your health care provider if acute painful crises occur or at the first sign of any infection.

Prevention

Sickle cell anemia can only result when two carriers with sickle cell trait have a child together. Therefore, genetic counseling is recommended for all carriers of sickle cell trait (about 1 in 12 African Americans has sickle cell trait).

Prenatal diagnosis of sickle cell anemia is also available. Prompt treatment of infections, adequate oxygenation, and preventing dehydration may prevent sickling of red blood cells. Antibiotics and vaccinations may prevent infections.

General health visits with a physician are recommended to ensure the patient is getting adequate nutrition, maintaining proper activity levels, and receiving proper vaccinations.