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HIV Serology

The ELISA (Enzyme-Linked Immunoabsorbent Assay) test is used to screen blood products and individuals at increased risk for HIV infection. 

If positive (reactive), the test is usually repeated on the same blood sample. Although this is a sensitive test, it is not highly specific for HIV (other conditions may give a positive ELISA). 

For that reason, before HIV can be confirmed, an additional test is performed, either:

  • Western Blot (WB), or
  • Indirect Fluroescent Antibody (IFA)

If either the WB or IFA is positive, the diagnosis of HIV infection is confirmed.

In the event the ELISA is positive, but the WB or IFA is negative, a repeat of the WB or IFA in 3-6 months is often recommended.

Normal Values*

ELISA Negative 
Western Blot Negative 
Indirect Fluroescent Antibody Negative

*These are general values taken from a variety of sources. The actual normal values may vary from lab to lab and from one type of testing protocol to another.

Source: Operational Medicine 2001,  Health Care in Military Settings, NAVMED P-5139, May 1, 2001, Bureau of Medicine and Surgery, Department of the Navy, 2300 E Street NW, Washington, D.C., 20372-5300