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Difficulty: EasyInfectious Diseases

A 24-year-old man comes to the clinic with fever, myalgias, and a rash 14 days after high-risk sexual exposure. Acute human immunodeficiency virus (HIV) infection is suspected. Arrange the following steps of the HIV diagnostic and initial management algorithm in the correct chronological sequence, assuming each diagnostic test yields a result consistent with acute HIV infection.

  1. 1Perform HIV-1/2 antigen/antibody combination immunoassay
  2. 2Perform HIV-1/HIV-2 antibody differentiation immunoassay
  3. 3Perform HIV-1 nucleic acid testing (NAT)
  4. 4Obtain baseline CD4 cell count, viral load, and genotypic resistance testing
  5. 5Initiate antiretroviral therapy (ART)

Answer

The correct chronological sequence is: 1) HIV-1/2 antigen/antibody combination immunoassay, 2) HIV-1/HIV-2 antibody differentiation immunoassay, 3) HIV-1 nucleic acid testing (NAT), 4) Obtain baseline CD4 cell count, viral load, and genotypic resistance testing, 5) Initiate antiretroviral therapy (ART).
The standard CDC algorithm for HIV testing begins with a 4th-generation HIV-1/2 antigen/antibody combination immunoassay. If positive, this is followed by an HIV-1/HIV-2 antibody differentiation immunoassay. In the setting of acute HIV infection, the differentiation assay is often negative or indeterminate because antibodies have not yet fully seroconverted. This requires resolution with an HIV-1 nucleic acid test (NAT) to detect viral RNA. Once acute HIV is confirmed, the standard of care is to immediately draw baseline labs (including CD4 count, viral load, and genotypic resistance testing) and subsequently initiate rapid or same-day antiretroviral therapy (ART) without waiting for the lab results.

Step-by-Step Solution

1
Identify the recommended initial HIV screening test.
HIV-1/2 antigen/antibody combination immunoassay.
This 4th-generation test is highly sensitive for early infection as it detects the p24 antigen before antibodies fully develop.
2
Determine the confirmatory test following a positive initial screen.
HIV-1/HIV-2 antibody differentiation immunoassay.
This step confirms the positive screening result and distinguishes the viral type, which impacts subsequent treatment choices.
3
Identify the necessary test to resolve a discrepancy in early acute infection.
HIV-1 nucleic acid testing (NAT).
In acute HIV, antibodies may be absent, causing a negative or indeterminate differentiation assay. NAT detects viral RNA to definitively confirm acute infection.
4
Sequence the pre-treatment evaluation.
Obtain baseline CD4 cell count, viral load, and genotypic resistance testing.
These baseline labs must be drawn after diagnosis but prior to starting therapy to guide long-term management.
5
Determine the final clinical intervention.
Initiate antiretroviral therapy (ART).
ART should be started as soon as possible, ideally on the same day the diagnosis is confirmed, to reduce the viral reservoir and decrease transmission risk.

Key Concept

HIV Diagnostic Algorithm and Rapid Antiretroviral Therapy Initiation
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Topics

Infectious Diseases

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