Hemophilia refers to a group of bleeding disorders in which there is a deficiency of one of the factors necessary for coagulation of the blood. Although the symptomatology is similar despite the missing factor, the identification of specific factor deficiencies has allowed definitive treatment with replacement agents. The two most common forms of the disorder are classic hemophilia (hemophilia A or factor IX deficiency). The following discussion is primarily concerned with the classic form, which accounts for about 75% of all cases.
A major feature of hemophilia is that its expression varies markedly in the degrees of bleeding severity. Hemophilia is generally classified into three groups according to the severity of factor deficiency.
1. Severe defects with less than 1% of the normal amount of factor; affected individuals bleed spontaneously or from minor trauma and literally may die from exsanguinations
2. Moderate defects with levels of 1% to 5% affected individuals usually bleed after some type of trauma but do not bleed spontaneously
3. Mild defects with levels ranging between 5% and 25% affected individuals manifest bleeding tendencies after they sustain a serious injury or undergo surgery, such as dental extraction or tonsillectomy.
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