Sickle Cell Anemia is an inherited disorder in which red blood cells contain an abnormal form of hemoglobin, a protein 
that carries oxygen. The abnormal form of hemoglobin causes the red cells to become sickle- or crescent-shaped. The misshapen cells may clog blood vessels, preventing oxygen from reaching tissues and leading to pain, blood clots and other problems (source: medical-dictionary.thefreedictionary.com).
Normal adult hemoglobin, designated hemoglobin A, consists of two 
-globin chains and two β-globin chains. The cause of sickle cell anemia is a point mutation in the β-globin gene. Orah S. Platt, M.D from the Department of Laboratory Medicine, Children’s Hospital Boston, as the author of the following article reviewed and discussed the clinical problem and the mechanism of benefit of the form of therapy follows, major clinical studies, the clinical use of therapy, and potential adverse effects, relevant formal guidelines, and ended with author’s clinical treatment recommendations.
According to the article, generally one with this disorder have a chronic hemolytic anemia, but the rates of the most common acute vaso-occlusive events (acute painful crises and the acute chest syndrome) vary considerably.
Cytotoxic effect of hydroxyurea reduces the production of red cells containing a high level of sickle hemoglobin, which tend to arise from rapidly dividing precursors, and favors the production of red cells containing a high fetal hemoglobin level (F cells), which arise from progenitors that divide less rapidly. This drug also reduces the numbers of white cells and platelets, potentially reducing their roles in vascular injury, accordingly.
Find completely about Sickle Cell Anemia, Treatment and Guideline here (source: nejm.org). Also you might find similar Anemia Journal in this site.
