What can be observed in a blood test?

Eosinophilia and mild non-regenerative anemia are common in cats infected with filariasis.
Neutrophilia, monocytosis, thrombocytopenia, and disseminated intravascular coagulation (DIC) occasionally occur when there is advanced arterial disease and pulmonary thromboembolism.
Hyperglobulinemia is rare.
Microfilaremia is rare and transient.
Blood tests are not useful for the diagnosis of filariasis.