Serology cannot be used reliably in domestic cats because reference intervals for babesiosis-related serologic titers have not been established.
Identifying intracellular piroplasms within erythrocytes on a Romanowsky or Giemsa-stained peripheral blood smear can be difficult as small piroplasms can be morphologically indistinguishable and the level of parasitemia may be low. Subsequently, the best strategy for definitive diagnosis of intraerythrocytic piroplasms is by molecular methods.
Polymerase Chain Reaction (PCR) detection of Babesia spp. DNA is a useful technique to document infection in a blood sample.