A paper published in Sexually Transmitted Diseases finds that commercial blood tests commonly used to diagnose herpes simplex virus (HSV) are frequently not reliable, especially in those with “low positive” results.

Herpes detection in people without symptoms typically involves a blood test to find HSV-specific antibodies that the immune system produces in response to the virus. Results with these tests (known as enzyme-linked immunoassays or EIA) are reported as an index value where the antibody levels are measured. An index value above 1.1 is considered positive, but some experts regard values less than 3.5 as “low positive” and recommend a confirmatory test such as the HSV Western Blot, long considered the gold standard with regards to accuracy and consistency of results.

Researchers from the University of Washington in Seattle and the Westover Heights Clinic in Portland, OR found that patients with low positive HSV-2 results on commercial EIAs frequently tested negative with the more sensitive Western Blot. With HSV-1, the reverse was true: commercial tests often overlooked HSV-1 antibodies later found with the Western Blot. In a press release issued by the University of Washington Health Sciences, study lead author Anna Wald, MD, said “These findings indicate that if you didn’t have signs and symptoms of genital herpes and were diagnosed by an (immunoassay antibody) test alone and had a low positive index value, there’s a 50-50 chance the test was wrong…In that case, you should get a confirmatory test.”

Read more about HSV diagnostics from the University of Washington Virology Research Clinic. Also browse resources offered through ASHA’s Herpes Resource Center.