Coombs' testing and its diagnostic significance in dogs and cats.

The Coombs' test can detect both immunoglobulin and complement on the surface of RBCs, and as such can be of value as an aid in the diagnosis of IMHA. Techniques that may improve sensitivity include use of monovalent reagents, increased dilutions of antiglobulin to avoid a prozone effect, and testing at 4°C. These techniques are not without controversy, and positive tests should always be interpreted in the presence of other clinical and hematologic evidence for IMHA. Alternate techniques, such as flow cytometry, can improve detection of RBC-bound immunoglobulin, but require a flow cytometer and further standardization between laboratories.