Sickle Cell Anemia
→ At least 40% and often more of RBCs contain an abnormal beta chain, known as Hemoglobin S.
→ When exposed to low O2 content, these beta chains contract, changing the shape of the cell to that of a sickle.
→ This causes these RBCs to stick and clump together, occluding the vessel and leading to further tissue hyposia.
→ Extensive periodic sickling (weekly to yearly) is called a crisis.
→ Eventually these crisis infarct more areas of organs such a spleen, liver, heart, kidney, brain, bones & retina leading to organ failure.
→ In sickle cell disease, the Pt has 2 HbS gene alleles, one from each parent, resulting in 80-100% of RBCs containing HbS.
→ In sickle cell trait, the Pt has 1 HbS gene allele and only half the RBCs will be defective so the person with trait will have only mild manifestations.