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OneLiner

Hemophilia A and B are deficiencies of factor VIII and IX, respectively. Both of these factors are part of the intrinsic coagulation pathway and so deficiency leads to an increase in aPTT. Since PT only tests fidelity of the common or extrinsic pathway (I, II, V, VII, and X), it is unaffected in Hemophilia A or B. Platelet count would not be affected by either disorder as they only affect coagulation factors.