Blockers

Passive blockers (e.g., mouse IgG, goat IgG) bind to non-specific sites or interfering antibodies in the sample to reduce background noise. Active blockers, such as TRU Block, contain targeted formulations designed to neutralize specific interfering antibodies like HAMA or RF, offering a higher degree of protection in complex sample matrices.

Mouse IgG is a passive blocker that helps reduce HAMA interference by competitive binding but may require high concentrations that can affect assay performance.
TRU Block^™ is an active blocker designed to more effectively neutralize a broader range of interfering antibodies, including HAMA and RF, even at lower concentrations.
Use Mouse IgG for general interference protection; choose TRU Block^™ for high-risk samples or when stronger, more targeted blocking is needed—such as in post-COVID or autoimmune populations.

Blockers are commonly used in ELISA, lateral flow assays (LFAs), and chemiluminescent immunoassays (CLIA)—particularly in sandwich and antibody capture formats where interference is more likely to generate false positives.

It depends on:

• Species of your assay antibodies
• Assay format (e.g., sandwich vs. competitive)
• Sample type (e.g., serum, plasma, whole blood)
• Known sources of interference (e.g., RF, HAMA)

Contact Meridian’s technical team for blocker recommendations tailored to your assay type.

Human anti-mouse antibodies (HAMA) is the most common antibody interference which causes both positive and negative interferences in two-site mouse monoclonal antibody-based assays.

No. HAMA only represents one type of heterophilic antibody (HA) interference – others include HA to animals such as goat (HAGA), sheep (HASA), and rabbit (HARA) which can cause false results when antibodies originating from these animals are used in immunoassays. In addition to HA there is another class of interference called Rheumatoid factor (RF), which is an autoantibody that reacts with the patient’s own immunoglobulin (Ig) and can cross-react with animal Ig, similar to HA/HAMA interference.

Rheumatoid factor is an autoantibody directed against the Fc portion of IgG. The most common type and main concern in immunoassay interference is IgM RF because it’s a pentamer—this makes it highly effective at crosslinking and forming immune complexes. IgM RF is common in people with rheumatoid factor, occurring in about half of all people with the disease, but about 1 in 20 people without rheumatoid arthritis can also have high levels, and is more common in elderly patients.

RF, similar to heterophilic antibodies, has the potential to cause falsely elevated test results by cross-linking the assay antibodies, even in the absence of analyte, most often via binding to the Fc-part of assay antibodies. RF can react against different species of IgG, including human and rabbit.

COVID-19 has led to a rise in circulating autoantibodies—particularly polyreactive forms of IgM rheumatoid factor (RF)—which can interfere with immunoassay performance. To protect assay accuracy, many developers are now validating with post-COVID clinical samples and incorporating high-performance blockers to mitigate the risk of false positives.