Final answer:
A complete blood count (CBC) would assist the physician in making a tentative diagnosis of leukemia.
Step-by-step explanation:
The exam that would assist the physician in making a tentative diagnosis of leukemia in this client would be a complete blood count (CBC). A CBC measures the levels of different types of blood cells, including red blood cells, white blood cells, and platelets, which can provide valuable information about the presence of abnormal cells in the blood, such as those seen in leukemia.