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•  Interpretation of the results of an ELISA diagnostic test

An enzyme-linked immunosorbent assay (ELISA) is a test that uses enzymes and colour changes to identify a substance

  • It can be used to identify specific surface markers or metabolites associated with particular diseases

Different variations of the ELISA test exist, but one of the most common protocols involves the sandwich method:

  • Known monoclonal antibodies are affixed to wells in a plate (these are the 'capture antibodies')
  • A sample to be tested is added to the wells and any antigens present will bind to the appropriate capture antibody
  • The plates are then washed to remove any unbound antigen
  • A second set of monoclonal antibodies linked to colour-changing enzymes are then added to the wells
  • These 'detection antibodies’ will bind to any antigens captured, creating a sandwich (antibody - antigen - antibody)
  • The wells are then washed again to remove any unbound detection antibodies
  • When an appropriate substrate is added to the wells, the enzyme-linked detection antibodies will trigger a colour change
  • Only wells in which a sandwich complex has formed will show a colour change, hence identifying the presence of an antigen

Summary of the Sandwich ELISA Method


Interpreting ELISA Tests

ELISA tests can be used to diagnose disease conditions based on the presence of disease markers (antigens, metabolites)

  • Samples taken from infected patients will induce a colour change when treated with appropriate detection antibodies
  • The amount of colour change can be used to signify rate of disease progression (more marker = more colour change) 

Results of an ELISA Diagnostic Test  (click on the diagram to solve)

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