Many people who carry sickle cell trait don’t know it. Yet, it can be just as deadly as sickle cell anemia.
In the United States, about 80,000 people have sickle cell anemia, but more than 12 million have sickle cell trait. Both disorders target certain ethnic groups, including South and Central Americans, Cubans, Saudi Arabians, Asians, Mediterraneans, and American Indians, but the disorders disproportionately strike African Americans. About 1 in 400 African Americans have sickle cell disease. About 1 in 10 African Americans have sickle cell trait.
What causes sickle cell disorders
Both sickle cell anemia and sickle cell trait are genetic disorders. People with sickle cell anemia have inherited homozygous sickle hemoglobin genes (hemoglobin S) from both parents; their blood type is called hemoglobin SS. People with sickle cell trait have inherited a normal hemoglobin gene (hemoglobin A) from one parent and a sickle hemoglobin gene from the other parent; their blood type is called hemoglobin AS.
Sickle cell anemia is a general term for several genetic disorders caused by red blood cells (RBCs) that are sickle-shaped because of deformed hemoglobin. A chronic condition, sickle cell anemia causes life-threatening signs and symptoms, such as an enlarged spleen, muscle pain, liver scarring, pneumonia, and bone and joint pain. The typical lifespan for those with sickle cell anemia is 40 to 60 years.
Screening for sickle cells
Two laboratory tests, Sickledex and hemoglobin electrophoresis, are used to screen for sickle cell anemia and sickle cell trait.
Sickledex detects sickle cells if 25% or more of RBCs have a sickle shape. Hemoglobin electrophoresis is much more sensitive: It can detect a small number of sickle cells. It also determines if a person has one or two mutated genes, thus distinguishing sickle cell trait from sickle cell anemia. Because the less sensitive Sickledex is less expensive, it’s commonly used for screening.
If one or both parents have sickle cell trait, a newborn needs genetic testing because early diagnosis helps prevent complications.
New view of sickle cell trait
Until the 1980s, sickle cell trait was considered a carrier state and a benign condition. But researchers who were investigating why young, healthy, African-American recruits were dying during military training discovered that 50% of them had sickle cell trait.
Today, people with sickle cell trait are considered to be at risk for death if they perform strenuous exercise without proper conditioning, become dehydrated, have an increased body temperature, participate in high-altitudes training, or exercise after an illness with a fever.
Sickle cell trait doesn’t cause obvious signs and symptoms, but in certain situations it may behave like sickle cell anemia with serious consequences. For example, some people with sickle cell trait have experienced abdominal pain at high altitudes and required a splenectomy. None of them had a clue they had sickle cell trait until they had this experience. Others learn they have sickle cell trait late in life when they have an illness that causes dehydration or fever. Still others find out at a health fair screening.
Why does sickle cell trait behave like sickle cell anemia?
People with sickle cell trait have both normal and abnormal RBCs, but usually both types are round. Round RBCs move easily through the tiny capillaries of the body. Unfortunately, when the abnormal RBCs are exposed to conditions that lead to hypoxia or dehydration, their shape changes from round to crescent or sickle-shaped. These sickle cells don’t transport as much oxygen as round cells, and they have difficulty moving through capillaries. Thus, body cells suffer from hypoxia both because of diminished oxygen transport and because of capillary blockage by the sickle cells. Unrelieved hypoxia progresses to cell death, excruciating pain (sickle-cell crisis), lactic acidosis, muscle and organ damage, and ultimately death.
When a person exercises, oxygen needs increase, and some cells may experience hypoxia. The hypoxia is more profound when a person exercises at high altitudes, where the atmospheric oxygen concentration is low. Any exercise causes perspiration and dehydration as the body attempts to cool itself. Perspiration is especially profound when a person is not conditioned, exercises strenuously, or exercises in a hot, dry environment.
How deadly rhabdomyolysis develops
A person with sickle cell trait who engages in strenuous exercise also can develop exertional rhabdomyolysis, the catabolism of muscle tissue—a potentially fatal condition. Rhabdomyolysis occurs when dehydration leads to sickle cells. When a person exercises, muscle protein breaks down and produces a waste product called myoglobin. If myoglobin production is excessive, and the body doesn’t have enough fluid to dilute it, myoglobin rises to toxic levels that damage the kidneys. Signs and symptoms of rhabdomyolysis include muscular swelling, muscular weakness, cramping, and pain. The urine looks like tea because it contains a large amount of myoglobin.
Treatment is based on symptom severity and is needed immediately to improve the chance of survival. The patient remains on bed rest and restricts all activity to decrease the workload on the affected body systems. The patient receives oral fluids and I.V. infusions to promote myoglobin excretion. For the same reason, a patient may receive a diuretic and sodium bicarbonate.
Preventing complications
No standard recommendations exist to decrease the risks for those with sickle cell trait, but certainly better screening and education would help. People need to know whether or not they have sickle cell trait. Because Sickledex can’t detect most cases of sickle cell trait, hemoglobin electrophoresis should be used for screening. When this test determines that a person has sickle cell trait, the person needs up-to-date information about the condition, including genetic counseling.
Athletic trainers, team physicians, coaches, and military drill instructors should be taught about sickle cell trait and the dangers of dehydration, the need to adjust to a new climate or higher altitude, the importance of physical conditioning, and the importance of rest during and immediately after an acute illness. Athletes who have sickle cell trait should inform coaches and trainers.
Many people have the trait and don’t know it, and those who do know may have been told it’s benign. But now we know better. We need more effective screening and patient teaching to manage the condition and prevent deadly complications.
References
Asgharian A, Anie K. Women with sickle cell trait: reproductive decision-making. J Reprod Infant Psychol. 2003;21(1):23-34.
Cleary M. Sickle cell trait and exertional rhabdomyolysis. Athletic Therapy Today. 2003;8(5):66-77.
Kark J. Sickle cell trait. Available at: http://sickle.bwh.harvard.edu/sickle_trait.html. Accessed May 20, 2007.
Platt A, Sacerdote A. Hope and Destiny: A Patient’s and Parent’s Guide to Sickle Cell Disease and Sickle Cell Trait. Roscoe, Ill: Hilton; 2002.
Phyllis Adams, EdD, RN, FNP, APRN, BC, NP-C, is Director of the Family Nurse Practitioner Program at the University of Texas at Arlington School of Nursing and a Family Nurse Practitioner at HEB School-Based Clinic in the John Peter Smith Health Network System, Euless, Texas.
