Blockers

Immunoassays used for human in vitro diagnostics (IVD) typically use animal-derived antibodies to recognize specific disease markers. Some patients have antibodies in their blood that can react with animal antibodies in the immunoassay and cause a false result. Although the frequency of these interferences is low, false-positive results have a significant negative impact on the quality and competitiveness of a diagnostic assay as well as on the lives of those individuals who have been falsely diagnosed.

Human anti-mouse antibodies (HAMA) is the 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 (usually IgM) directed against the Fc portion of IgG. It 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.

Our recommendations are: a) use the species of the blocker the same as the host of the capture or detection antibody; 2) use at a concentration of Mouse or Goat IgG equivalent to ten times the concentration of the MAb/PAb being used in the assay. (e.g. if 5ug/mL of Ab/conjugate, add 50ug/mL of animal IgG)