Diagnosis

In 2014, CDC updated its recommendations for HIV testing to improve the accuracy of laboratory diagnosis of HIV infection based on testing of serum or plasma specimens.24 Laboratory criteria for defining a confirmed case now accommodate new multi-test algorithms, including criteria for differentiating between HIV-1 and HIV-2 infection and for recognizing early HIV infection (Figure 1). To adapt to these changes, CDC also revised the surveillance case definitions for HIV infection.9

Figure 1. Recommended Laboratory HIV Testing Algorithm for Serum or Plasma Specimens.9,24

Diagram showing recommended laboratory HIV testing algorithm for serum or plasma specimens

A confirmed case of HIV infection is now classified in one of five stages (0, 1, 2, 3, or unknown).9 Early infection, i.e., a negative HIV test within 6 months of HIV diagnosis, is classified as stage 0. If the criteria for stage 0 are not met, the stage is classified as 1, 2, 3, or unknown depending on CD4+ T-lymphocyte test results or whether an opportunistic illness was diagnosed >180 days after the diagnosis of HIV infection (Table 3). Acquired immunodeficiency syndrome (AIDS) is classified as stage 3.

Table 3. Case classification of HIV infections (persons ≥6 years of age).9
Stage 0 No opportunistic illnesses If >180 days have elapsed after stage 0 at diagnosis, the stage at the later date is classified as 1, 2, 3, or unknown
Stage 1 No opportunistic illnesses Either CD4+ T-lymphocyte count of ≥500 cells/μL or CD4+ T-lymphocyte percentage of total lymphocytes ≥26
Stage 2 No opportunistic illnesses Either CD4+ T-lymphocyte count of 200-499 cells/μL or CD4+ T-lymphocyte percentage of total lymphocytes of 14-25
Stage 3 (AIDS) At least one opportunistic illness Either CD4+ T-lymphocyte count of <200 cells/μL or CD4+ T-lymphocyte percentage of total lymphocytes of <14.*
Stage unknown No information on opportunistic illnesses No information on CD4+ T-lymphocyte count or percentage.
*Documentation of opportunistic illnesses (Table 1) supersedes a CD4+ T-lymphocyte count of >200 cells/μL or CD4+ T-lymphocyte percentage of total lymphocytes of >14.