Aspirin per se does not affect the total leukocyte count (TLC), though it affects the platelet function. He would require a complete blood count (including red cell indices), a differential leukocyte count (DLC) and a peripheral blood film (PBF) examination to know the cause of leukocytosis. The possibility of chronic myeloid leukaemia and chronic lymphocytic leukaemia need to be ruled out, which a PBF examination would do.