A saline agglutination test is a very easy in-house diagnostic procedure
and should be performed in any patient with suspected hemolytic anemia.
It is redundant if gross agglutination is noted in the CBC sample or the hematocrit tube.
Simply place a drop of EDTA blood on to a microscope slide.
Add a drop of 0.9% NaCl and mix it with the blood.
Look under the microscope at the red blood cells.
Check for agglutination, which is characterized by persistent clumping of cells.
If you disturb the slide, the cells will stay attached to each other.
It can be difficult to differentiate rouleaux formation from true agglutination because these processes can look similar at first glance.
However, cells in rouleaux tend to stack rather than clump, and they dissipate when disturbed.
Remember that a positive saline agglutination test indicates that there are antibodies on the surface of the erythrocytes.
This supports a diagnosis of immune-mediated hemolytic anemia (IMHA).
However, positive agglutination tests can occur in patients with other causes of hemolysis, such as zinc ingestion or erythrocyte parasitism.
Conversely, some dogs with IMHA do not have a positive saline agglutination test, so a negative result does not exclude this diagnosis.