Serologic tests for the diagnosis of HIV-1 or HIV-2 infection. A. Algorithm including the use of a Western blot. *Stable indeterminate Western blot 4-6 weeks later makes HIV infection unlikely. However, it should be repeated twice at 3-month intervals to rule out HIV infection. Alternatively, one may test for HIV-1 p24 antigen or HIV RNA. EIA, enzyme immunoassay. B. CDC algorithm not including the use of a Western blot. (Adapted from CDC Stacks: Quick reference guide-Laboratory testing for the diagnosis of HIV infection: updated recommendations 2014. Available from http://stacks.cdc.gov/view/cdc/23446.)