Final answer:
A medical assistant should use an antiseptic solution to prepare a patient's skin for drawing blood cultures to reduce the risk of microbial contamination.
Step-by-step explanation:
When drawing blood cultures, a medical assistant should prepare a patient's skin using an antiseptic solution. Alcohol swabs, commonly made with alcohols like ethanol, are useful for degerming the skin before needle injections because of their bactericidal and fungicidal properties. However, for blood cultures, it is important to use an antiseptic that will not only cleanse but also reduce the risk of contamination by microorganisms. Products like iodine-based solutions or chlorhexidine are often used as antiseptics for this purpose, providing a broader spectrum of microbial kill prior to a blood draw.