Situation: A 34-year-old man was diagnosed with human immunodeficiency virus (HIV) infection 1 week ago and has enrolled at a Department of Health (DOH)–accredited treatment hub, where he starts the once-daily tenofovir–lamivudine–dolutegravir (TLD) tablet today. His CD4 count is 150 cells/mm³, he has never had an opportunistic illness, and he has no drug allergies. How should the nurse classify the stage of his infection based on these data?

Acquired immunodeficiency syndrome (AIDS), or stage 3 HIV infection, is defined by a CD4 count below 200 cells/mm³ OR an AIDS-defining illness. Either criterion is enough, so a count of 150 cells/mm³ classifies him as having AIDS even without an opportunistic illness. The date of diagnosis does not define the stage, because infection may have been present for years before testing.

Stage classification in HIV infection

HIV disease is staged by the degree of immune damage, not by how recently the diagnosis was made. The two accepted ways to define acquired immunodeficiency syndrome (AIDS), also called stage 3 HIV infection, are a CD4 count below 200 cells/mm³ or the presence of an AIDS-defining opportunistic illness. These criteria operate independently, so meeting either one is sufficient.

In this case, the CD4 count is 150 cells/mm³, which falls below the 200 cells/mm³ threshold. Even though the man has never had an opportunistic illness, the CD4 value alone places him in the AIDS category. The fact that he was diagnosed only 1 week ago does not change the staging, because HIV may have been present for years before testing. A person can therefore present with advanced immunosuppression at the time of first diagnosis.

Watch out! The cutoff is not 100 cells/mm³. A CD4 count below 200 cells/mm³ is the standard threshold for AIDS in the classification system used by the U.S. Centers for Disease Control and Prevention and in most licensure examination contexts. Some countries use different operational definitions for treatment eligibility, but that does not alter the staging definition being tested here.

The relationship between CD4 count and clinical outcomes supports why this threshold matters. In a cohort of 1,604 HIV-seropositive men followed over 10 years, lower CD4 lymphocyte counts were associated with a higher risk of HIV-associated neurologic complications such as dementia and sensory neuropathy ^[1]. This illustrates that CD4 depletion is not merely a laboratory number; it reflects meaningful immune compromise that increases vulnerability to serious disease. The CD4 count is therefore used as the primary marker of immunosuppression because it correlates with the risk of clinical deterioration.

A separate analysis reinforces that CD4-defined disease status remains central to clinical decision-making. In a study of HIV-infected individuals in Brazil, CD4 count was used as the reference marker for defining disease status, and hematologic and soluble adhesion molecule profiles were examined in relation to that CD4-based classification . Although Brazil applies a stricter public health threshold for AIDS (CD4 < 350 cells/mm³) than the WHO criterion (CD4 ≤ 200 cells/mm³), the underlying principle is the same: the CD4 count is the anchor for staging HIV disease and for determining the degree of immunosuppression. For licensure examination purposes, the widely used staging definition remains a CD4 count below 200 cells/mm³.

Key point! Staging is based on objective immunologic or clinical criteria, not on the date of diagnosis or the absence of symptoms. A patient with a CD4 count of 150 cells/mm³ has AIDS by laboratory criteria even if he feels well and has no opportunistic infection.

The role of CD4 testing in guiding care is also well established in resource-limited settings. In pregnant and postpartum women with HIV, CD4 cell count testing was more effective than clinical staging alone in identifying those eligible for antiretroviral therapy . This reinforces that CD4 count is a practical, objective tool for classifying disease severity and initiating treatment, which is exactly what this patient is beginning today with the once-daily tenofovir–lamivudine–dolutegravir (TLD) regimen.

The incorrect options can be ruled out systematically. Option 1 is wrong because an opportunistic illness is not required when the CD4 count is already below 200 cells/mm³. Option 3 is wrong because the threshold is 200 cells/mm³, not 100 cells/mm³. Option 4 is wrong because acute HIV infection refers to the early symptomatic phase soon after viral acquisition, and the timing of diagnosis does not override the immunologic staging criteria. The correct classification is AIDS, stage 3, based on the CD4 count of 150 cells/mm³.