Hemophilia A

At a glance

Most severe hereditary coagulation disorder. It is caused by defective synthesis of plasma protein factor VIII. The condition must be suspected in the presence of prolonged bleeding following a venepuncture or simple heel prick at the time of birth.

Synonyms

Classical Hemophilia; F-VIII Deficiency.

Incidence

1:5000 to 10,000 live male births; 30% of cases are the result of new mutations.

Genetic inheritance

X-linked recessive with expression in male children only. Gene locus is Xq28. Although in the majority of cases it is inherited as an X-linked recessive trait, cases that arise from spontaneous mutations have been reported.

Pathophysiology

Defective factor VIII gene produces low levels of functional factor VIII. Factor VIII is required in the intrinsic coagulation cascade and, when activated and in the presence of factor XIa, leads to activation of factor X. Affected patients are classified as mild, moderate, or severe. Mildly afflicted patients have factor VIII levels 6 to 30% of normal activity and experience hemorrhage secondary to trauma or surgery, but rarely spontaneously. Patients moderately afflicted have factor VIII levels of 1 to 5% of normal activity and experience hemorrhage secondary to trauma or surgery with occasional spontaneous hemarthroses. Severely afflicted patients have less than 1% of normal factor VIII activity and experience frequent spontaneous hemorrhages from early infancy requiring replacement therapy. Although carriers usually have 50% normal activity and experience no bleeding difficulties, levels should be obtained, as those with less than 50% activity can experience significant hemorrhage after trauma.

Diagnosis

Elevation of the partial thromboplastin time with normal prothrombin time and normal bleeding time. Diagnosis is established by dosage of factor VIII antigen and factor VIII serum factor activity. Prenatal and carrier detection are possible with restriction fragment length polymorphism DNA analysis but are contingent upon parental analysis.

Clinical aspects

Soft tissue hematomas, including retroperitoneal/pharyngeal hemarthroses (75%), most often of the same target joint, pseudotumor of bone, with rare erosion into viscera, hematuria, intracranial hemorrhage, cord compression secondary to epidural bleeding, nerve compression secondary to hematoma, mucous membrane hemorrhage (epistaxis, hemoptysis), peptic ulcer disease, and excessive postsurgical bleeding.

Precautions before anesthesia

Hematology and anesthesiology consultation are highly recommended before elective surgical procedures. Schedule procedures early in the week to avoid weekend pharmaceutical delays. Ensure supply of virally inactivated or recombinant factor VIII concentrate, which does not have the infectious risks of fresh-frozen plasma or cryoprecipitate. Dose calculations are based on the following formula: 1 unit factor VIII/kg increases factor VIII activity by 2%. Half-life is 8 to 12 hours. Consider desmopressin acetate (DDAVP 0.3 μg/kg) in mild-to-moderate disease because it increases factor VIII levels up to ...