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Etiology of Sickle Cell Crisis

The clinical manifestations of sickle cell anemia vary markedly in severity and frequency. The most acute symptoms of the disease occur during periods of exacerbation called crises. There are four types of episodic crises vaso-occlusive, splenic sequestion, aplastic, and hyperhemolytic crises.

Vaso-occlussive crises are the most common and the only painful ones. They are the result of sickled cells obstructing the blood vessels, causing occlusion, ischemia, and potentially necrosis. The major symptoms of this crisis are fever, acute abdominal pain from visceral hypoxia, hand-foot syndrome, and arthralgia, without an exacerbation of anemia.

Splenic sequestration crises are caused by the spleen sequestering (pooling) large quantities of blood, causing a precipitous drop in blood volume and ultimately shock. The crisis may be acute or chronic. The chronic manifestation is termed functional asplenia. The acute form occurs most commonly in children between 8 months and 5 years of age and may result in death from profound anemia and cardiovascular collapse.

Aplastic crisis is diminished red blood cell production, usually triggered by a viral or other infection. When superimposed on the existing rapid destruction of red blood cells, a profound anemia results.

Another type of bone marrow crisis is megaloblastic anemia, which is attributed to an excess nutritional need for folic acid/ or vitamin B12 during periods of pronounced erythropoiesis. Since infection is not always antecedent to aplastic or hypoplastic crises, it is possible that folic acid deficiency is a causative agent.

Hyperhemolytic crisis occurs when there is an even greater rate of red blood cell destruction. It is characterized by anemia, jaundice, and reticulocytosis. It is a rare complication and frequently suggests other coexisting abnormalities, such as glucose-6-phosphate dehydrogenase deficiency, which is also common in black persons.

Diagnostic evaluation
Although sickle cell anemia has been reported during the neonatal period and early part of infancy, it may not be recognized until the toddler and preschool period. It is frequently first diagnosed during a crisis, after an acute upper respiratory or gastrointestinal infection. Crisis, after an acute upper respiratory or gastrointestinal infection.

Several tests are available for detecting sickle cell anemia. Although most of the routine hematological tests described are done primarily to evaluated the anemia, this discussion focuses on the four tests specifically used to detect the homozygous or heterozygous for of the disease. For screening purposes either the sickling test of the sickledex is commonly used. If the test is positive, hemoglobin electrophoresis is necessary to distinguish between those children with the trait and those with the disease. Screening for sickle cell trait has become a controversial subject, especially among the black community, since there is no method of preventing the disease other than selective birth procedures.

Stained blood smear
Examination of the stained smear of blood may reveal a few sickled red blood cells. However, since the erythrocyte assumes its normal discoid shape under adequate oxygenation, non-sickled cells may be present even in the homozygous form of the disease. Whenever sickle cells are found, the diagnosis is usually positive for sickle cell anemia, not sickle cell trait.

Sickling test (sickle cell slide preparation)
The simplest method to detect sickling is to place a drop of blood on a slide and cover it with a sealed cover slip to produce de-oxygenation. Eventually sickling of the red blood cell occurs. Unfortunately this test may take several hours before results are obtained, and it is not specific for the disease or trait. False negatives for the trait can occur if the blood contains a very small amount of hemoglobin S.

Hemoglobin electrophoresis (“fingerprinting”)
In this test, the blood is specially prepared and separated into various hemoglobin by high-voltage electrophoresis. The resulting pattern of the separated peptides as it appears on paper is referred to as “fingerprinting” of the protein.

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