How to Perform a Slide Agglutination Test in a Dog

Cost

Free for Elite Members

July 2024

In this VETgirl online veterinary continuing education video, Dr. Amy Kaplan, DACVECC at Urgent Pet Care, demonstrates how to perform a slide agglutination test (also called a saline agglutination test) in a dog. This is a very cost-effective, easy-to-perform test that can easily be done in practice and should be done in a patient with a high index of suspicion for immune-mediated hemolytic anemia (IMHA). This may be seen with a low PCV, normal TP, and icteric serum/mucous membranes. The slide agglutination test (often abbreviated a “SAG” or called a “slide agglut”) is used to determine if true autoagglutination is occurring (versus non-immune related causes for RBC adhesion, such as rouleux formation).

Generally, the slide agglutination test consists of placing 1 drop of anti-coagulated blood from a purple top tube (e.g., EDTA) or capillary tube on a slide and then 1-2 drops of 0.9% NaCl mixed on the slide(some references utilize 1-2 drops of saline in dogs, and 3-4 drops in cats due to their RBCs being more likely to develop rouleaux formation). The slide is rocked back and forth gently for a few seconds while looking for macroagglutination (You would be able to see gross macroagglutination with the naked eye). If you don’t see this, a coverslip can be placed on the slide and microscope evaluation for microagglutination should be performed (typically considered more than 4-5 RBCs clustered together like grapes). This microagglutination is different from the classic “stack of coins” RBC which is consistent with rouleaux. If microagglutination is observed, or if you have questions as to whether you are seeing rouleaux versus agglutination, then the next step is to dilute the sample further with 0.9% saline to try to “break up” the rouleaux as described in this video; true autoagglutination will not disperse and break up with additional saline. So, based on the newest recommendations, dilute your sample (1:9, if not more!) as shown here, to try to take away factors that may create a false appearance of agglutination, and look under that ‘scope again!

Rouleaux can further be differentiated from autoagglutination by adding additional saline and by RBC washing techniques; extra saline often disperses rouleaux but will not disperse true autoagglutination. Keep in mind that running a SAG may or may not confirm IMHA; if agglutination is seen, that is consistent with IMHA; however, since a positive SAG is typically only seen with high RBC antibody levels, a negative SAG doesn’t rule out IMHA and should be followed up with a Coombs and additional testing.

 

Not a VETgirl ELITE member? Get your learning on with the #1 veterinary CE resource – clinically relevant, practical, and accessible 24/7 on your own time! Don’t miss out – click HERE to check out your options, including our new  14-day, no-commitment ELITE Trial.

Only VETgirl members can leave comments. Sign In or Join VETgirl now!