Why isn't western blot testing used more often to confirm the ELISA HerpeSelect antibody test for HSV 2?
Only in the past few years have we recognized that there can be some false positives on the ELISA test. These most often occur in test sample where the index value that fall between 11 and 3.5. False positives over 3.5 are very rare. At our clinic, every person who has an index value between 1.1 and 3.5 is advised to get western blot confirmation. There are other tests that can be used for confirmation, like the BioKit, but we prefer the western blot as the gold standard confirmatory test.
There are probably several reasons this test is not used more often. First, I don't think that most clinicians have any idea about false positives on the ELISA. The test is reported out as positive if the index value is above 1.1, and that's the end of it for most clinicians. For them, an index value of 1.2 is as definitive as a 4.8. But this is just not so. So there is lack of awareness on the topic.
Second, western blots are labor intensive, not automated, and they are done only at the University of Washington in the US, so samples must be shipped there. Quest labs offers western blot reference testing in most states, but six states won't allow samples to be sent out of the state to UW for testing.
Third, the code for herpes western blot testing is not in the normal lab books; you have to know about it and find out a way to get the code for ordering (it is 34534). Other labs, like LabCorp, another very large lab system, will send the western blot to UW, but only with great difficulty - it has no code available for routine ordering at the time of this writing but the test may be obtained by writing in the name “herpes western blot to University of Washington”. Companies that offer online herpes antibody testing also don't offer herpes western blot confirmation - the first one that does will have a lot of business!
Fourth, many clinicians have no idea what a western blot test is - they think it's a test for HIV infection. Instead, it is a method of testing that can detect different infections, including herpes, HIV and others. It is not a test for a specific disease.
In summary, there is lack of awareness about false positives, lack of ease of ordering the test, and lack of knowledge about the western blot among clinicians. The need for education for clinicians in this area is huge. If they understood the implications and rate of false positives in this low positive range, they could drive laboratory availability and awareness.
-- Terri Warren, RN, ANP
Owner, Westover Heights Clinic in Portland Oregon