An HIV-positive patient asks you if you can tell him the chances of him progressing to symptomatic AIDS. Which one of the following tests would be most useful?

HIV PCR, a nucleic acid amplification test for HIV RNA, has recently been shown to be the most valuable test for: monitoring a patient's progress during triple drug therapy and determining the chances of progression to AIDS. A viral load of 750,000 copies per ml significantly increases the chance of progression to AIDS within 5 years. The other tests listed do not accurately predict progression to AIDS.