Diagnosis

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). In 2023, the CDC updated its recommendations for HIV testing to provide guidance on the use of HIV NATs (nucleic acid tests) with a diagnostic claim in the third step of the current recommended algorithm for laboratory testing.¹³

Figure 1. Recommended Laboratory HIV Testing Algorithm for Serum or Plasma Specimens.¹³

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.

0/17Next