Final answer:
Susan's increased bleeding is indicative of a potential vitamin K deficiency. Antibiotics can affect gut flora and subsequently vitamin K production, which is crucial for blood clotting. Her doctor will need to assess her platelet function and vitamin K levels among other factors.
Step-by-step explanation:
Given that Susan is 72 years old and has been on antibiotics for nearly three weeks, and observing her increased bleeding upon sustaining cuts, a vitamin deficiency related to blood clotting is suspected. The essential vitamin for the clotting process is vitamin K. Antibiotics can sometimes disrupt the gut flora, which is important for vitamin K production. Furthermore, vitamin K is paramount for the synthesis of certain clotting factors. A deficiency in vitamin K can result in prolonged bleeding because it is vital for converting fibrinogen into fibrin, thus leading to an effective clot formation. Susan's concern about the need to frequently replace her bandaid due to continued bleeding suggests that her blood clotting mechanisms may indeed be compromised, and this could potentially be linked to a deficiency in vitamin K, among other possibilities that her doctor needs to investigate.
Platelets, or thrombocytes, also play a crucial role in clotting as they adhere to the site of injury, release their contents, and interact with clotting factors to form a platelet plug. Susan's doctor may need to evaluate her overall health including, but not limited to, platelet function, the use of any other medication that could interfere with blood clotting, such as aspirin, and her diet to ensure she has adequate vitamin K intake.