The presence of Heinz bodies in erythrocytes indicates:
Individuals with inherited deficiency of G6PD, an enzyme required for hexose monophosphate shunt for glucose metabolism, fail to develop adequate levels of reduced glutathione in their red cells. 
This results in oxidation and precipitation of hemoglobin within the red cells forming Heinz bodies.

​Mohan H. Textbook of pathology. Jaypee Brothers Medical Publishers; 2015. Edition 7. Page 293
Malarial infection
Hemoglobin abnormalities
Oxidative stress
Degraded bacterial forms