The Two-Tiered Serologic Testing Algorithm: Understanding ELISA and Western Blot Protocols
When the characteristic rash is absent or a patient presents with systemic symptoms, clinicians rely on the Two-Tiered Testing (2TT) paradigm. This protocol is designed to maximize both sensitivity (detecting the disease) and specificity (avoiding false positives).
First Tier: Enzyme-Linked Immunosorbent Assay (ELISA): This initial screen measures the total concentration of antibodies against Borrelia proteins. It is highly sensitive but can cross-react with other conditions, such as syphilis or autoimmune disorders.
Second Tier: Western Blot or Immunoblot: If the ELISA is positive or equivocal, a Western Blot is performed. This test separates the bacteria's proteins into "bands." For a diagnosis to be confirmed, a specific number of these bands must show antibody activity. For example, the CDC requires 5 out of 10 specific IgG bands to be present for a "positive" late-stage result.