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Enzyme-linked Immunosorbent Assay

Sound Diagnostics uses ELISAs to measure antibodies to the organisms which cause various infections in rabbits and rodents. ELISAs are performed as illustrated:

 
ima1p ima2p ima3p ima4p ima5p ima6p
FIG.1. FIG.2. FIG.3. FIG.4. FIG.5. FIG.6.

ELISAs are relatively easy and inexpensive to perform. The amount of antibody is quantitated by optical density (O.D.) and compared to positive and negative controls.

Ranges of negatives and positives for each of the assays have been established from control sera. There are no "normal ranges" as with serum chemistry values. Uninfected animals will have a negative titer.

Negative results indicate a lack of antibodies to the antigen at that point in time. In the early stage of infection, the amount of antibodies may be below the level of detection. False negative results may occur when immunocompromised animals produce inadequate amounts of antibodies.

Equivocal (suspicious) results are usually clarified by a follow-up sample. For infections in the early stage, antibody levels will be considerably higher in the follow-up sample. If the antibodies are due to non-specific reactivity or past infection, values will remain about the same.

Positive results indicate infection, but not necessarily disease. However, high levels of antibodies may be associated with disease. Antibody levels may decrease with time if the infection has been eliminated, but months are usually required.

Using these guidelines, ELISAs are useful in determining infection and possible association with disease.
 


*Kendall, LV and Riley, LK. Enzyme-linked immunosorbent assay (ELISA). Contemporary Topics 1999; 38: 46-47.