CD4 Testing: A Critical Diagnostic Tool for Advanced HIV

On World AIDS Day last December, leading HIV experts Anthony Fauci, MD, and Greg Folkers, MS, MPH, warned that stalled US funding could unravel decades of progress in the fight against HIV/AIDS. Globally, the HIV epidemic remains a major public health challenge: in 2024, more than 40 million people were living with HIV, with 1.3 million new infections and 660,000 deaths reported that year.

In 2025, the World Health Organization reaffirmed something many clinicians on the frontlines of HIV care have long understood: CD4+ T-cell testing remains essential for identifying and managing advanced HIV disease. 

These updated recommendations clarify the distinct and complementary roles of CD4 testing and viral load monitoring in comprehensive HIV care.

Defining advanced HIV disease

When a person living with HIV presents with a CD4 cell count below 200 cells per cubic millimeter of blood, they are diagnosed with advanced HIV disease (AHD). 

This threshold is clinically significant. It signals not only disease progression but also heightened vulnerability to life-threatening opportunistic infections such as tuberculosis, cryptococcal meningitis, and pneumocystis pneumonia. 

The WHO now defines AHD for adults and adolescents as having a CD4 count below 200 cells/mm³ or WHO clinical stage 3 or 4 disease, while all children under 5 years of age living with HIV are considered to have advanced disease.

Recent fieldwork in Southeast Asia revealed the real-world consequences when CD4 testing is unavailable or underutilized. Healthcare providers described patients presenting with severe opportunistic infections that could have been diagnosed with earlier identification of their immune status. 

In the Philippines and Indonesia, where tuberculosis incidence remains high among people living with HIV, the absence of baseline CD4 testing creates critical gaps in patient care.

The evolving role of CD4 testing

The journey of CD4 testing in HIV care guidelines reflects the complexity of managing chronic disease in resource-varied settings. 

Prior to 2015, CD4 counts were the primary criterion for determining when to start antiretroviral therapy (ART). The 2015 WHO "treat all" guidelines shifted focus toward immediate treatment regardless of CD4 status, which inadvertently led some programs to deprioritize CD4 testing entirely.

However, clinical evidence has consistently demonstrated that CD4 testing remains the best predictor of disease status and immediate risk of death in HIV patients. 

The 2025 WHO recommendations now explicitly state that "CD4 testing is recommended as the preferred method to identify advanced HIV disease among people living with HIV."

A comprehensive approach to HIV care

Modern HIV care requires multiple diagnostic tools working in concert. 

While viral load monitoring tells us whether antiretroviral therapy is effectively suppressing the virus, CD4 testing provides crucial information about immune function and detection of ART failure, and disease stage. 

This dual approach is particularly vital for vulnerable populations.

For infants born to mothers living with HIV, the stakes are especially high. Research shows significantly elevated mortality rates in HIV-positive children under 2 years of age who are not receiving therapy. 

Yet globally, only approximately 60 percent of children born to HIV-positive mothers receive appropriate early infant diagnosis. The window for intervention is narrow—young immune systems are uniquely vulnerable to rapid HIV progression.

Real-world implementation challenges

Infrastructure and access remain significant barriers in many high-burden regions. In Southeast Asia, where HIV cases continue to rise, particularly among young adults aged 25–35, many patients face difficult choices between affording transportation to testing facilities and other basic needs. 

Stigma compounds these challenges, with individuals often traveling long distances to seek testing away from their communities.

Recent advances in diagnostic technology are helping address these barriers. Integrated testing approaches that combine molecular testing for viral load with automated flow cytometry for CD4 counting can now deliver comprehensive results within approximately 90 minutes. This enables clinicians to assess both viral suppression and immune status in a single patient visit, facilitating faster clinical decision-making and appropriate care.

Renewed emphasis on CD4 testing

The renewed emphasis on CD4 testing represents more than updated guidelines. It reflects a maturing understanding that effective HIV care requires comprehensive, patient-centered approaches. 

As we work toward ending AIDS as a public health threat, we must ensure that all diagnostic tools, including CD4 testing, are accessible to those who need them most.

The path forward demands continued innovation in making diagnostics more accessible, sustained funding for HIV programs, and ongoing education about the critical role of immune monitoring in preventing opportunistic infections and reducing mortality. 

Only by maintaining this comprehensive approach can we ensure that people living with HIV receive the life-saving care they deserve.