Comprehensive HIV laboratory testing: Screening, prevention, and care to drive better outcomes and reduce transmission

Despite advances in understanding, preventing, and managing HIV infection, approximately 1.2 million Americans are infected with HIV.¹ That number is on the rise in the US, with about 32,000 new HIV infections diagnosed in 2022.¹ Research reveals ongoing differences in the impact of HIV, with an estimated 70% of new infections in 2022 occurring among Black and Hispanic Americans.¹

HIV testing continues to be an important factor in both prevention and treatment efforts, supporting awareness of infection and maximizing treatment options through earlier detection.

Pre-exposure prophylaxis (PrEP) is an important tool to prevent the transmission of HIV, but many who could benefit from the medication have not been prescribed it.²

By following CDC guidelines for HIV prevention, including the CDC-recommended fourth-generation HIV screening algorithm, physicians can identify infection and initiate appropriate interventions, driving progress in curtailing the continuing epidemic.

In this article:

Clinical challenge | Why it matters | Ordering recommendations | Next steps | Supporting resources

Clinical challenge: closing gaps in HIV infection awareness and treatment

In the midst of rising HIV infection in the US, nearly 160,000 people are unaware that they have HIV. This group transmits nearly 40% of new HIV infections.³ Closing this gap of awareness represents a significant step forward in slowing the spread.

In terms of prevention, effective measures such as pre-exposure prophylaxis (PrEP) are available. However, while PrEP medications could benefit an estimated 1.2M people in the US, fewer than 36% of those currently take this type of prescription.⁴ This presents an opportunity to reverse the trajectory of infection further.

New research underscores the importance of starting treatment early.² Anti-retroviral therapy (ART) can be very effective in reducing viral load to undetectable levels when started as soon as possible during acute infection, when symptoms of HIV can include flu-like symptoms (eg, fever, headache, and rash).⁵

However, across the continuum from HIV diagnosis to viral suppression, there are missed opportunities for addressing the epidemic. According to the CDC, while many people with HIV are diagnosed (87%), far fewer receive medical care (66%), and fewer still are virally suppressed (57%). Viral suppression is greater among those who are in medical care, but social barriers can impede engagement with care.²

Why it matters: Screening and prevention are among the most powerful tools for ending the epidemic

Despite continuing transmission, gaps in awareness of HIV infection and in the prescription of preventive medications like PrEP represent significant opportunities to slow the spread. Diligent, guideline-supported screening leads to identification and treatment of patients with HIV infection, which can help reduce transmission, morbidity, and related complications.⁶

Early, consistent engagement in treatment gives individuals with HIV optimal care outcomes including improved health, quality of life, and life expectancy, as well as offering preventive benefits. When an individual with HIV is consistently managing the infection with antiretroviral therapy and the level of HIV in their body is undetectable, there is effectively no risk of sexual transmission.²

Additionally, there are systemic supports in place to encourage engagement with testing and treatment. HIV screening and linkage to care is a quality metric for community health centers, and PrEP medication and testing are covered under ACA, with $0 cost-sharing.

Ordering recommendations: Fourth-generation HIV screening algorithm

• One-time testing is recommended for all individuals age 13-65⁷
• People engaging in risky behaviors should get tested at least once every year⁸

All adults can benefit from following CDC guidelines for HIV screening and monitoring⁹

Individuals suitable for testing

• Pregnant individuals, including those who are in labor or delivery
• Individuals 13 to 65 years of age
• Individuals at increased risk of HIV infection
• Children ≥2 years of age with suspected HIV infection

Recommended test (screening):

HIV Screen:

HIV-1/2 Antigen and Antibodies, Fourth Generation, with Reflexes

Test code: 91431

HIV-1 and HIV-2 RNA, Qualitative Real-Time PCR
Test code: 14312

Recommended test (monitoring):

Viral load monitoring:

HIV-1 RNA, Quantitative, Real-Time PCR
Test code: 40085

Recommended test (HIV PrEP):

PrEP HIV-1/2 Antigen and Antibodies, Fourth Generation, Screen and HIV-1 RNA
Test code: 13590

PrEP HIV-1/2 Antigen/Antibodies, 4^th Generation, Reflex to Differentiation
Test code: 13595

PrEP HIV-1 RNA, Qualitative Real-Time PCR
Test code: 13600

PrEP HIV-1/2 Antigen and Antibodies, Fourth Generation, with Reflexes
Test code: 13670

PrEP HBV Triple Screen Panel with Reflexes
Test code: 13660 (includes HBV Surface Antigen with Reflex Confirmation, HBV Core Antibody, Total, with Reflex to IgM, HBV Surface Antibody, Quantitative)

PrEP Hepatitis C Antibody with Reflex to HCV, RNA, Real-Time PCR
Test code: 13667

PrEP RPR (Diagnosis) with Reflex Titer and Treponema pallidum Antibody, IA
Test code: 13698

PrEP Chlamydia/Neisseria gonorrhoeae RNA, TMA, Urogenital
Test code: 13701

PrEP Creatinine
Test code: 13697

PrEP hCG, Total, Quantitative
Test code: 13696

Chlamydia/Neisseria gonorrhoeae RNA, TMA, Throat
Test code: 70051

Chlamydia/Neisseria gonorrhoeae RNA, TMA, Rectal
Test code: 16506

Clinical background

The US Preventive Services Task Force and CDC recommend HIV screening for everyone age 15 to 65 and for people who are pregnant, using an opt-out approach.^6,10 More frequent screening and screening younger children or older adults may be appropriate based on individual risk assessments.^6,10 Detecting HIV infection during the acute phase (before seroconversion) is important because this phase is marked by high viral load and contributes disproportionately to transmission.^10,11 In addition, HIV testing is recommended immediately before starting pre-exposure prophylaxis (PrEP) for HIV and regularly thereafter because taking PrEP during acute HIV infection may induce resistance to antiretroviral drugs.¹²

The CDC recommends an HIV diagnostic testing algorithm based on fourth-generation antigen/antibody (Ag/Ab) combination assays (Figure).^11,13 The first step in the algorithm is a fourth-generation Ag/Ab assay, which simultaneously detects HIV-1 p24 antigen and HIV-1/2 antibodies. Because the p24 antigen is detectable before seroconversion, this type of assay can detect HIV-1 in the acute phase of infection.¹¹ The inclusion of HIV-1 and HIV-2 antibodies allows detection after seroconversion, when the p24 antigen becomes undetectable. Fourth-generation Ag/Ab assays have >99.7% sensitivity and >99.5% specificity for HIV infection¹¹ and can identify most (>80%) acute infections that would otherwise require nucleic acid testing for detection.¹⁴ The fourth-generation assay used by Quest Diagnostics requires repeat testing of reactive (positive) results before reflexing to supplemental testing.

To confirm repeatedly reactive results from fourth-generation Ag/Ab assays, the CDC recommends using an HIV-1/HIV-2 antibody differentiation assay as a supplemental test.^11,13 Differentiating HIV-1 and HIV-2 can have treatment implications, as HIV-2 does not respond to some antiretroviral agents.¹¹ However, HIV-1/HIV-2 antibody assays may yield negative results during acute infection before seroconversion. Thus, HIV-1/HIV-2 RNA testing is used as the last step in the algorithm to resolve infection status for people with repeatedly reactive HIV Ag/Ab results but negative or indeterminate HIV-1/HIV-2 antibody results.^11,13 In accordance with the latest guidance from the CDC,¹³ results for HIV-1 and HIV-2 RNA are individually reported.

Next steps:

Continue regular lab testing to monitor immune status and viral load. Follow CDC-recommended screening for coinfections with other blood-borne pathogens.

Immune status

The most valuable indicator of immune status and the strongest predictor of disease progression and survival in HIV-positive patients is the CD4+ T-cell (CD4) count.¹⁵ Once a patient is diagnosed with HIV, baseline CD4 counts should be measured and then monitored every 3-6 months in patients who do not immediately begin anti-retroviral therapy (ART).¹⁵

Viral load

HIV-1 viral load is the primary marker of ART effectiveness. Before treatment begins, the viral load provides information on the risk of disease progression, helps to inform treatment selection, and establishes a baseline for assessing treatment response.¹⁵ After treatment has begun, measuring viral load helps assess therapy efficacy.

When initiating ART or changing regimens due to inefficacy, lab testing is an important tool for selecting drug regimens. Such tests include genotypic HIV resistance to identify drug resistance-associated mutations, HIV-1 coreceptor tropism testing to help determine eligibility for treatment with CCR5 antagonists, and HLA-B*5701 typing for genetic risk stratification prior to initiation of Abacavir therapy.

Comorbidities

The CDC recommends that all individuals infected with HIV be tested for hepatitis B virus (HBV) and hepatitis C virus (HCV). Approximately 2% of people with HIV in the US also have HBV, and HCV coinfection occurs in nearly 75% of people with HIV who also inject drugs. People with HIV are at greater risk for complications and death from HBV and/or HCV infection.¹⁶

Additionally, the CDC recommends that all sexually active persons with HIV be screened for syphilis, gonorrhea, and chlamydia first at the initial care visit and then on an annual basis. Women should also be screened for trichomoniasis at these same intervals. Those at an increased risk for STIs should be screened more frequently based on their individual risk.¹⁷

Supporting resources: