HIV 4th Generation Test (Antigen and Antibodies)
A fourth-generation HIV test looks for two things in one blood sample: the p24 antigen, a protein that can appear early after exposure, and antibodies to HIV-1 and HIV-2, which the immune system produces later. Checking both is what allows this test to be informative sooner than antibody-only testing.
About this test
Testing for HIV is an ordinary part of health care. Many people include it in a routine check-in, after a new partner, before starting a relationship, or simply because they like knowing where they stand.
The fourth-generation format combines two markers. The p24 antigen is part of the virus itself and can be present in blood relatively early.
Who might consider this test?
- People order this test for all kinds of ordinary reasons: routine sexual health maintenance
- A conversation with a partner about testing together
- A recent situation they want clarity about
Test details
| Quest code | 91431 |
|---|---|
| Methodology | Immunoassay |
| Sample type | 3 mL serum |
| Collection | Quest patient service center |
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Additional details
What the two parts of the test look at
The antigen portion looks for p24, a viral protein that can appear in blood within the first weeks after infection. The antibody portion looks for the immune system's response to HIV-1 and HIV-2, which typically becomes measurable somewhat later. Combining them into one assay is what makes this a fourth-generation test.
Because the two markers appear on different timelines, a single negative result taken very soon after a possible exposure does not close the question. This is the window period, and a clinician can advise when a follow-up test would give a clearer picture.
Screening first, confirmation second
This is a screening assay, and screening assays are deliberately built to be sensitive. A reactive result is a signal that further, more specific laboratory testing is warranted — it is not a conclusion, and it is not a diagnosis. Supplemental testing that a clinician orders is what clarifies the picture, and that follow-up process is well established and routine.
Understanding this ahead of time takes some of the tension out of testing. The screening step exists to decide whether more information is needed, and a clinician guides whatever comes next, whether that is confirmation, repeat testing, or nothing further at all.
Privacy and how results are handled
Your sample is collected at a patient service center with the same discretion given to any other laboratory work, and the requisition does not announce what is being tested to anyone in the waiting room. Your report is delivered securely to you, and you decide who sees it.
Reviewing a result privately, on your own time, makes the process easier for many people. If you would like help interpreting it, sharing the report with a clinician is straightforward — and worth doing, since context matters.
Cost and ordering without insurance
The cash price shown next to the order button is the full amount, with the physician's order included and no insurance billed. There is no consultation appointment to schedule and no referral to obtain. Sample collection is available at Quest patient service centers, , so the whole process usually takes minutes.
Order online and a physician order is included — no doctor's visit and no insurance needed. Your sample is collected at a Quest Diagnostics patient service center.
Laboratory results should always be interpreted by a licensed clinician who knows your health history. This page is information about a test, not medical advice.
Frequently asked questions
What does a fourth-generation HIV test look for?
It looks for two markers in one blood sample: the p24 antigen, part of the virus that can appear early, and antibodies to HIV-1 and HIV-2 produced by the immune system later. Checking both is what makes it informative earlier than antibody-only testing.
How much does an HIV test cost?
The cash price is shown next to the order button on this page and includes the physician's order. No insurance is billed, so nothing appears on an insurance statement, and there is no separate doctor's visit fee.
How long after a possible exposure should I test?
Both markers take time to become measurable, so testing very soon after an exposure may not reflect it. A clinician can advise on timing for your situation and whether a repeat test later would add useful information.
Is a reactive screening result a diagnosis?
No. A reactive screen prompts additional, more specific laboratory testing that a clinician arranges. Diagnosis is made by a clinician who reviews confirmatory results together with your history, not by a screening result alone.
Will anyone else see my result?
Your report is delivered securely to you as a PDF. Sharing it with a clinician, a partner, or anyone else is entirely your choice.
Do I need a doctor's appointment to order this?
No. The physician's order is arranged as part of the purchase, so you can order online and go straight to a patient service center for the blood draw.