ELISA Test

This week the owner and head veterinarian of the clinic took some time to show me how to use the blood analysis machines.  The clinic relies heavily on these machines to measure blood cell count, check enzyme and hormone levels, and detect parasites and diseases.  These tests are performed routinely throughout the day, and quick results within minutes ensure that clients are provided with conclusive data to back up diagnoses.  I found the test kits used along with these machines to be particularly interesting.  The clinic uses IDEXX SNAP Tests to screen for many different diseases including, Parvovirus, heartworms, Lyme disease, FIV (Feline Immunodeficiency Virus), and FeLV
(Feline Leukemia Virus).  These tests are a simple plastic tray in which a sample, in this case blood, is added to a sample well, the tray is snapped down into place, and within minutes results can be interpreted by the appearance of blue dots in the sample window.  It sounds simple enough, but there is actually more to these tests than one might think.  Having been exposed to similar types of tests before in class this past semester, I quickly recognized that these SNAP Tests were actually ELISA tests.  The ELISA, or enzyme-linked immunosorbent assay, is a test that uses antibodies (proteins produced by the body to identify foreign substances) and color change to detect and identify the presence of a substance, usually an antigen (proteins present on foreign substances like viruses and bacteria that stimulate an immune response).

Here's how the ELISA technology works within these SNAP Tests:

1. A sample and a conjugate are combined in a sample tube.  The conjugate contains an antibody with a specific enzyme linked to it.  This enzyme antibody complex binds to specific antigens in the sample.

2. The sample tube's contents are poured into the sample well and flow across the surface of the test tray.  The conjugate/antigen complex binds to antibody present on the test surface.

3. The device tray is pressed down into place until a snap is heard.  The sample flows across the test surface once again in the opposite direction to provide plenty of time for the conjugate/antigen to bind to the antibody.

4. A wash solution clears debris that may interfere with results.

5. A colorless substrate following the wash interacts with the conjugate enzymes.  The enzymes convert the substrate molecules from colorless to a blue, amplifying signal.  This reaction forms blue dots in the results window for easy interpretation.  Each test has a positive control spot that will show, but any color development in the sample spots indicate the presence of specific antigens.

 

IDEXX SNAP Test with test tray, pipette, blue conjugate, and sample tube