Sickle cell anemia (SCA)

Abstract:
Sickle cell anemia belongs to the hemoglobinopathies. A point mutation (β6Glu->Val) leads to the formation of an abnormal β-chain, the so-called hemoglobin S. Deoxygenated HbS tends to aggregate in long polymers. This causes the erythrocytes to lose their deformability and to take on the sickle form. These erythrocytes become sequestrated in the reticulo-endotheliomal system (extra-vascular hemolysis) or may lead to occlusions in small vessels (infarctions). Sickle cell anemia occurs most commonly in people from sub-Saharan Africa, the Caribbean and parts of Asia. In central India, the prevalence is the world's highest with 30%. The high prevalence in tropic countries is explained by a certain protection from malaria. The fact that absence of oxygen leads to the sickling of erythrocytes, is used in the laboratory for the sickle cell test. The definitive diagnosis is determined by means of hemoglobin electrophoresis.

Clinical picture:
Sickle cell anemia is the homozygous form. The heterozygous form is called sickle cell-trait. In spite of hemoglobin concentration between 60 and 100 g/L, there are few symptoms of anemia, due to the early disassociation of oxygen in the HbS. Sickle cell crises are characteristic of sickle cell anemia. These entail acute, painful, episodes caused by occlusions of small vessels. They are usually brought on by infections or exposure to the cold. All organs can be affected by these vascular occlusions. In children, this results in different growth lengths of fingers and toes. A feared complication is the acute chest syndrome, in which disorders of pulmonal pulmonale microcirculation lead to respiratory failure. This is the main cause of death in SCA. Cholelithiasis occurs often as a result of chronic hemolysis. Similar to spherocytosis, infections by parvovirus B₁₉ can lead to aplastic crises.

Hematology:

In the blood film, the characteristic sickle cells as well as target cells can be found. In adults, functional asplenia is often present due to the recurrent splenic infarctions. Howell-Jolly-bodies and Pappenheimer bodies can be seen. The number of sickle cells can vary from a few up to 40%. There is reticulocytosis with normoblasts, polychromasia and increased RDW. An increased LDH, increased bilirubin and low haptoglobin are sign of hemolysis. Typically, HbS accounts for 90-95% in the Hb-elektrophoresis.