A student asks the nurse at the student health clinic how HIV is diagnosed. Which of the following statements would be the best response by the nurse?

"A diagnosis of HIV is made when CD4 T-lymphocytes drop to less than 30 cells/mm."

"A diagnosis of HIV is made when antibodies to HIV reach peak levels of 1000/ml of blood."

"A diagnosis of HIV is made when a patient tests positive for Syphilis."

"A diagnosis of HIV is made when antibodies to HIV are detected (seroconversion) about 6 weeks to 3 months following possible exposure."