Difference Between Sickle Cell Trait and Sickle Cell Anemia

Difference Between Sickle Cell Trait and Sickle Cell Anemia

Anemia is defined as a condition in which the concentration of hemoglobin or the number of red cells in blood are decreased below normal value either singly or in combination. It is usually interpretated by measuring hemoglobin concentration. Anemia is a global problem most marked in infants and children and also in women during child bearing period.

It affects children of poor socio-economic group and it may be associated with other diseases such as protein energy malnutrition. Anemia may result from poor production of cells, or defective cells, or due to excessive loss by hemorrhage or destruction of red cells by excessive haemolysis. Anemia may be classified on the basis of etiology, or morphological characteristic.

Classification according to types of hemoglobin:

Etiological Classification

  1. Nutritional
  2. Hemolytic
  3. Bone marrow depression
  4. Blood loss or hemorrhagic
  1. Nutritional anemia: Due to deficiency or low intake of iron, folic acid, vitamin B12, ascorbic acid, pyridoxine and trace elements.
  2. Hemolytic anemia


Sickle hemoglobin (Hb S) differs from normal adult hemoglobin by a substitution of glutamic acid at the 6th position of its beta chains by valine. In the oxygenated state Hb S functions normally and there is propensity of deoxygenated hemoglobin S to polymerize. Polymerization of sickle hemoglobin distorts erythrocyte morphology, decreases red cell deformability, causes a marked reduction in the red cell life span, increases blood viscosity and predisposes to episodes of vaso-occlusion.

Sickle cell disease is a chronic illness that comes from two parents who have sickle cell trait. This disease can be passed on if both parents have a sickle cell trait & give that child each trait. The sickle cell trait is important because one must know if he/she is a carrier. If you carry this trait, most likely you will not be sick. It is only when you have children that knowing if you carry the trait is vital. Your child could be born with a painful, chronic, underexposed illness that will require that you have more knowledge than most doctors. Arm yourself with knowledge & get ready for a long fight for justice.

Unlike normal red cells, which are usually smooth and donut-shaped, sickled red cells cannot squeeze through small blood vessels. Instead, they stack up and cause blockages that deprive organs and tissues of oxygen-carrying blood. This process produces periodic episodes of pain and ultimately can damage tissues and vital organs and lead to other serious medical problems. Normal red blood cells live about 120 days in the bloodstream, but sickled red cells die after about 10 to 20 days. Because they cannot be replaced fast enough, the blood is chronically short of red blood cells, a condition called anemia.

Sickle cell disease affects more than 72,000 Americans, primarily those of African heritage, but also those of Arabian, Asian, Caribbean, Indian, Mediterranean, and South and Central American descent, Middle Eastern, India, Syrians, Turks, Cypriots, Sicilians, Caucasians, and others. Genetically, there are two types-

  1. Sickle cell trait and
  2. Sickle cell anemia.

Sickle Cell Trait:

Heterozygous state of the sickle gene is called sickle cell trait. Individuals have been shown to resist invasion by lethal plasmodium falciparum form of the disease. There is no anemia or haemolysis and physically normal Sickle trait erythrocyte are capable of sickling, particularly under condition of significant hypoxemia and a number of clinical abnormalities have been linked which includes splenic infarction or sequestration, hyposthenuria, painless hematuria, bacteriuria and pyelonephritis during pregnancy.

Under intense, stressful conditions, exhaustion, hypoxia (low oxygen), and/or severe infection, the sickling of the defective hemoglobin may occur and result in some complications associated with the sickle cell disease. Someone who inherits only one sickle cell gene and a normal gene from the other parent will have the sickle cell trait, but not the disease. A blood test can determine whether you have sickle cell disease or carry the sickle cell trait.

Carriers of the sickle cell gene are said to have sickle cell trait. Unlike sickle cell disease, sickle cell trait does not cause health problems. In fact, sickle cell trait is protective against malaria, a disease caused by blood-borne parasites transmitted through mosquito bites. Survivors pass the mutation on to their offspring, and the trait became established throughout areas where malaria was common.

Hemoglobin electrophoresis shows about 60% hemoglobin A and about 40% hemoglobin S with normal levels of hemoglobin A2 and hemoglobin F. A confirmatory solubility test excludes other abnormal hemoglobin with similar electrophoretic mobility. Neonatal screening programs for the detection of infants with sickle cell disease are widely established. These disorders can also be determined antenatally using aminocyte or chorionic villus DNA sampling. Each child has a 1 in 4 (25%) chance of having sickle cell anemia if both parents carry the sickle cell trait.

People with sickle cell trait usually do not have any of the symptoms of the disease. However, it is possible for a person with sickle cell trait to have complications of the disease under extreme conditions, such as; high altitude (flying, mountain climbing, or cities with a high altitude), increased pressure (scuba diving), low oxygen (mountain climbing or exercising extremely hard, such as in military boot camp or when training for an athletic competition), dehydration (too little water in the body). In addition, a person with sickle cell trait can pass the disease on to their children.

Sickle Cell Anemia (Homozygous Hb S):

Sickle cell anemia is caused by homozygosity for the sickle gene and is the most common form of the disease. The symptoms and signs of sickle cell disease are related to the hemolytic anemia and tissue ischemia and organ dysfunction caused by vaso-occlusion. Infants are not symptomatic until 3-4 months of age as high level of fetal hemoglobin inhibit sickling.

Sickle cell anemia, which is also known as meniscocytosis or sicklemia, is an inherited blood disorder that arises from a gene mutation. As a result, affected hemoglobin molecules have a tendency to stick to one another, forming abnormal strands of hemoglobin within the red blood cells. The cells that contain these strands become stiff and elongated—sickle-shaped.

There is pallor, fatigue, jaundice and gallstones during childhood and adolescents. Acute sickle dactylitis or hand-and-foot syndrome, recurrent ischemic pain particularly abdominal or musculoskeletal is very common. There is splenomegaly due to intense congestion by sickle cells and results in splenic infarction and sequestration, usually associated with pain causing autosplenectomy. These children are at risk of overwhelming infection (bacterial sepsis) with encapsulated bacteria. Acute pain episodes may progress to infarction of bone marrow or bone and avascular necrosis may develop in hip.

Painful crisis:

This is the most common and usually due to infarction either in bone, spleen or in the lung (the chest syndrome). The crisis provoked by infection, cold or dehydration. Acute splenic sequestration often occur and characterized by sudden enlargement of the spleen with pooling of red cells with resultant acute exacerbation of anemia, and in severe cases, shock and death. Acute exacerbation of anemia also occurs with aplastic crisis, usually caused by infection with human parvovirus and no reticulocyte response. The acute chest syndrome is characterized by fever, pleuritic pain and acute pulmonary infiltrates with hypoxemia caused by pulmonary infection, infarction, or fat embolism from ischemic bone marrow.

Hemolytic crisis is characterized by fall in hemoglobin, jaundice increases but there is a good reticulocyte response.

Strokes caused by cerebrovascular occlusion are a frequent cause of hemiplegia. Ischemic damage may also affect myocardium, liver and kidneys (hyposthenuria, polyuria). There is a complication that results from the pooling of blood in the corpora cavernosa, causing obstruction of the venous outflow and there may be decreased fertility. All tissues are susceptible to damage from vaso-occlusion and multiple organ dysfunctions are common in adulthood and chronic leg ulcers also common.

The hemoglobin level ranges between 7-9gm/dl. The anemia is usually normocytic or macrocytic and reticulocytosis. The peripheral blood smear typically contains target cells, poikilocytes, sickled cells. Nucleated red cells and Howell-Jolly bodies are often present. The total WBC count is elevated to 12,000-20,000/cmm, with a predominance of neutrophils. The platelet count is usually increased; the sedimentation rate is slow. Other changes include abnormal liver function, hyperbilirubinemia, and diffuse hypergammaglobulinemia. The bone marrow is markedly hyperplastic and shows erythroid predominance. X-ray show expanded marrow spaces and osteoporosis. X-ray hand is informative which shows evidence of extensive bony destruction and repair.

If one parent has Sickle Cell Anemia and the other is Normal, all of the children will have sickle cell trait. If one parent has Sickle Cell Anemia and the other has Sickle Cell Trait, there is a 50% chance (or 1 out of 2) of having a baby with either sickle cell disease or sickle cell trait with each pregnancy. When both parents have Sickle Cell Trait, they have a 25% chance (1 of 4) of having a baby with sickle cell disease with each pregnancy.

The diagnosis is established by hemoglobin electrophoresis where Hb S is 80-90%, Hb F - 2-20% and Hb A2 -2-4% and absent Hb A. The identification of Hb S in each parent provides additional supportive evidence.

HbA1c, also call A1C, is a measure of the amount of glucose attached to hemoglobin (Hb) in red blood cells. The higher the glucose levels over the previous 2-3 months, the higher the A1C. The A1C test is used to monitor the glucose levels of patients who have been diagnosed with diabetes. In people who have hemoglobin variants such as HbS (sickle cell trait) or HbC trait, some A1C tests give falsely high or low readings that can lead to the overtreatment or undertreatment of diabetes.


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