A diagnosis can be made by
The demonstration of gametocytes in blood smears.
Histopathological examination of the liver, spleen and brain can show developing megaloschizonts.
Necropsy may reveal an enlarged spleen and liver.
Since the majority of birds are sub clinically infected with Leucocytozoon, other causes of death must be ruled out even with the presence of Leucocytozoon gametocytes in peripheral blood smears.