Which test would most likely confirm a diagnosis of giardiasis?

The stool antigen test is the most appropriate choice for confirming a diagnosis of giardiasis because it specifically detects the presence of Giardia lamblia antigens in the stool. Giardiasis is an intestinal infection caused by the parasite Giardia, and this test is sensitive and specific, making it an effective tool for identifying active infections.

In contrast, the fecal occult blood test is primarily used to check for hidden blood in the stool, which is not directly related to diagnosing Giardia infection. A complete blood count provides general information about overall health and can help identify some signs of infection, but it does not provide specifics about Giardia. X-ray imaging is not utilized for diagnosing giardiasis, as it does not visualize the intestinal parasites or provide relevant diagnostic information for this type of infection. Thus, the stool antigen test stands out as the most targeted and reliable method for confirming giardiasis.