Final answer:
A positive response to HIV treatment is indicated by a decreased viral load, signifying successful control of the virus and preservation of the immune system.
Step-by-step explanation:
The positive response to prescribed HIV treatment in a patient is most accurately indicated by D. Decreased viral load. The goal of antiretroviral therapy is to impede viral replication, thus preserving the immune function by maintaining healthy levels of CD4 T cells. As these levels are sustained or improved, the viral load should decrease, reflecting effective control of the disease progression. A decrease in the number of circulating HIV particles is a key marker that the treatment regimen is successful. While increased creatinine clearance, changes in eosinophil levels, and decreased T cells are not direct indicators of positive treatment response, a decrease in viral load directly correlates with the effectiveness of the HIV therapy.