What is the significance of an 18 kDa (kilodalton) IgG (Immunoglobulin G) band reactivity in Lyme disease testing?

From the Guidelines

The presence of an 18 kD (IgG) band in Lyme disease testing is not a definitive diagnostic marker, as current guidelines require multiple reactive bands (typically 5 out of 10 specific IgG bands) to be considered positive, as stated in the study by 1.

Interpretation of Lyme Disease Test Results

The 18 kD band is not explicitly mentioned in the provided study as a specific diagnostic marker for Lyme disease. However, the study discusses the importance of interpreting Western immunoblot results based on the presence of multiple reactive bands.

• A positive IgG Western immunoblot result is indicated by the scored presence of >5 of 10 bands (18,21–24,28,30,39,41,45,58,66, and 93 kDa) 1.
• The study emphasizes the need to avoid interpreting fewer bands as a positive overall result or evidence of infection because antibodies to several antigens are cross-reactive with non-Borrelial antigens 1.

Clinical Implications

In clinical practice, the presence of an 18 kD (IgG) band should be considered in the context of the patient's overall clinical presentation, exposure history, and other laboratory findings.

• If a patient has a positive 18 kD band but does not meet the full diagnostic criteria, the doctor should interpret this result cautiously and consider other diagnostic possibilities 1.
• The study highlights the importance of using a 2-tiered testing approach, which includes an enzyme-linked immunosorbent assay (ELISA) or indirect fluorescent antibody (IFA) test, followed by a Western immunoblot test, to minimize false-positive results 1.

From the Research

Interpretation of 18 kd (IgG) Band in Lyme Testing

• The 18 kd (IgG) band is one of the protein bands that can be detected in Lyme disease testing, specifically in Western blot tests 2.
• Western blot tests are used to detect the presence of antibodies against Borrelia burgdorferi, the bacteria that causes Lyme disease.
• The presence of an 18 kd (IgG) band can indicate exposure to B. burgdorferi, but it is not a definitive diagnosis of Lyme disease.

Clinical Relevance of IgG and IgM Antibody Responses

• Studies have shown that IgG and IgM antibody responses to B. burgdorferi can vary after antibiotic therapy for erythema migrans, a common manifestation of Lyme disease 2.
• Some patients may have persistent positive IgG titers, while others may have persistent negative titers or a decrease in positive titers after therapy.
• The clinical relevance of these different antibody responses is not fully understood, but persistent positive IgG titers have been correlated with longer disease duration or larger EM lesions before therapy.

Limitations of Current Evidence

• There is limited research specifically addressing the 18 kd (IgG) band in Lyme testing, and more studies are needed to fully understand its clinical significance.
• Current evidence suggests that antibody testing, including Western blot tests, may not be reliable for assessing therapeutic response in patients with Lyme disease 2.