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Enzyme-linked Immunosorbent Assay (ELISA)*
Sound Diagnostics uses ELISAs to measure antibodies to the organisms which cause various infections in rabbits and rodents. ELISAs are performed as illustrated:
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.
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