Highest yield for parasite in case of Kala azar is obtained on:

Splenic aspiration is one of the most sensitive and widely used procedure and sensitivity may be as high as 95-97%. As a prerequisite for deciding splenic aspiration it is essential to determine prothrombin time and platelet count. If the prothrombin time is more than 5 seconds longer than the control sample and the total platelet count is less than 40000/cu.mm the splenic aspiration is contraindicated. Ref: