The current serologic testing for Lyme disease is a so-called two-tier test. This includes a first-tier screen with an EIA. If that is positive, you then do immunoblots — a bit of an old-fashioned technology — to look for specific antibodies against antigens. That methodology in most clinical settings means you don't get a result back for 3 to 7 days after obtaining a blood test because immunoblots usually take time to be batched and run.
In the newer, two-tier test, two EIAs are done either at the same time or sequentially. These are platforms that most labs can run in-house. You get results quickly the same day or the next day. Some of these modified two-tier tests use antigens that allow for earlier diagnosis after Lyme infection than standard tests. The reporting of positive or negative tests can usually be accomplished within a day or two, at most. Further, laboratories do not like doing immunoblots. They are a difficult technology and a bit more variable.
This kind of approach, which has been approved by the FDA for one company (though I’m sure others will seek approval as well) ultimately allows for a faster and likely less expensive diagnostic approach to Lyme disease testing. It's important to note that it's really hard to culture Lyme disease or to find that bacteria by a molecular technique, so we currently remain reliant on serologic diagnosis.
Clinicians should know that with modified two-tier testing used in a laboratory setting, you will still get a positive or a negative result. It is possible to still be in equivocal range on the first tier, and then have the second show as positive or negative. You will not see bands. As an infectious disease clinician, I find that patients and clinicians are often confused by reports that include bands.
How your lab runs the modified two-tier test is important because you have options to report either positive immunoglobulin M or immunoglobulin G antibodies. For someone who has symptoms for several weeks who you think may have an acute infectious illness, the modified two-tier approach works very well. If you think someone has long-term symptoms for weeks or months, you may still wish to get an IgM and IgG determination of antibodies because there are still high rates of false-positive IgM antibodies. For anyone with long-term symptoms, the combined test that includes both IgM and IgG may give you a false impression of Lyme disease.
As always, there are still, a couple of caveats with Lyme disease testing.
Paul G. Auwaerter, MD, MBA
Professor of medicine
Clinical director, infectious diseases division
Johns Hopkins University School of Medicine
Disclosures: Auwaerter reports working as a consultant for DiaSorin.