Examkin

Question

Difficulty: MediumOrdering Laboratory Tests

A 26-year-old man comes to the clinic requesting screening for sexually transmitted infections. He reports a new male sexual partner 3 weeks ago and notes one episode of unprotected insertive and receptive anal intercourse. He feels well and has no fever, rash, sore throat, or lymphadenopathy. Vital signs are within normal limits. The physician plans to evaluate the patient for human immunodeficiency virus (HIV). Arrange the following diagnostic laboratory tests in the correct sequential order according to the standard HIV testing algorithm.

  1. 1HIV-1/2 antigen/antibody combination immunoassay
  2. 2HIV-1/HIV-2 antibody differentiation immunoassay
  3. 3HIV-1 nucleic acid amplification test (NAT)

Answer

The correct sequence is: (1) HIV-1/2 antigen/antibody combination immunoassay, (2) HIV-1/HIV-2 antibody differentiation immunoassay, and finally (3) HIV-1 nucleic acid amplification test (NAT).
The Centers for Disease Control and Prevention (CDC) recommends a specific sequence for HIV diagnosis. Step 1 is the fourth-generation HIV-1/2 antigen/antibody combination immunoassay. If this is nonreactive, the patient is considered HIV-negative. If reactive, Step 2 is the HIV-1/HIV-2 antibody differentiation immunoassay. If this differentiation assay is reactive for either HIV-1 or HIV-2, the diagnosis is confirmed. However, if the differentiation assay is nonreactive or indeterminate, Step 3 is an HIV-1 nucleic acid test (NAT). This sequence efficiently balances diagnostic sensitivity, specificity, turnaround time, and cost.

Step-by-Step Solution

1
Select the initial screening test.
HIV-1/2 antigen/antibody combination immunoassay is placed as the first step.
Current guidelines recommend a fourth-generation assay detecting both p24 antigen and HIV antibodies as the most sensitive initial screening method, particularly for identifying early infection before seroconversion is complete.
2
Select the confirmatory test following a reactive screening test.
HIV-1/HIV-2 antibody differentiation immunoassay is placed as the second step.
A reactive initial screen requires confirmation. The differentiation assay confirms the presence of HIV antibodies and identifies the specific viral type (HIV-1 vs. HIV-2), which is critical for guiding antiretroviral therapy.
3
Select the test used to resolve discordant early results.
HIV-1 nucleic acid amplification test (NAT) is placed as the final step.
In early or acute infection, the p24 antigen may be positive on the screening test before enough antibodies develop to trigger a positive differentiation assay. A viral load assessment via NAT is required to resolve this discrepancy and confirm acute HIV-1.

Key Concept

The standard diagnostic algorithm for human immunodeficiency virus (HIV) involves sequential testing starting with a fourth-generation antigen/antibody combination assay, followed by a differentiation immunoassay, and culminating in a nucleic acid test to resolve indeterminate results.
Rate this question

Topics

Ordering Laboratory Tests

More questions from this topic