Borrelia burgdorferi IgM Western Blot

What is Borrelia burgdorferi IgM Western Blot?

Confirms IgM antibodies against Borrelia burgdorferi as part of two-tier Lyme testing, generally suggesting more recent exposure.

This Western blot identifies IgM antibodies against specific Borrelia burgdorferi proteins as part of the CDC-recommended two-tier testing process following a positive or equivocal screening ELISA. IgM antibodies typically appear earlier than IgG, so this test is most useful within the first several weeks of possible infection; CDC guidance notes that a positive IgM result is less reliable, and more prone to false positives, when used later in illness. It is commonly ordered together with the IgG Western blot after a positive or equivocal ELISA, particularly when a recent tick bite or early symptoms such as a rash or flu-like illness are present. Results are interpreted alongside the timing of exposure and the ELISA result rather than in isolation.

Tests often checked alongside this

• Borrelia burgdorferi Ab (Lyme ELISA) — the initial screening test this confirms
• Borrelia burgdorferi IgG Western Blot — considered together to build a fuller picture
• Anaplasma phagocytophilum Ab and Babesia microti Ab — possible co-infections

How this can show up in how you look and feel

• May be associated with an expanding rash at the site of a tick bite
• May be associated with fever, chills, headache, or muscle and joint aches
• May be associated with fatigue in the weeks following a tick bite

What can affect this marker

• Timing of testing relative to the tick bite or symptom onset is especially important for IgM interpretation
• Prior tick-borne exposure
• Immune status
• Lab-to-lab variability in Western blot band interpretation

What to track over time

• How this result relates to the timing of the original tick bite or symptoms
• Whether the ELISA and IgG Western blot results support this finding
• Whether repeat testing weeks later is useful if early testing was inconclusive
• How symptoms evolve over time alongside test results

What to ask your doctor

• Given the timing of my possible exposure, how reliable is this result?
• How does this fit with my ELISA and IgG Western blot results?
• Could this reflect a false-positive result given how IgM testing behaves later in illness?
• Is repeat testing recommended?

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