What laboratory test is used for detecting filariae in the blood?

Detecting filariae in the blood primarily involves the use of a blood smear. This method allows for the visualization of the adult worms or microfilariae (the larval stage) in the bloodstream. A blood smear can be examined microscopically, where the filarial larvae can often be identified based on their characteristic morphology. This is particularly useful in cases of infections like those caused by Wuchereria bancrofti, Brugia malayi, or Dirofilaria immitis, where the microfilariae circulate in the peripheral blood.

In contrast, other testing methods would not be suitable for this purpose. For example, stool sample analysis is used to detect gastrointestinal parasites and would not provide information on filarial infections. A urine test is typically employed for detecting urinary tract infections or specific urinary parasites but is not relevant to blood-borne filariae. Serological tests could provide information regarding the presence of antibodies to the filarial antigens in the blood; however, these tests do not directly visualize the filariae, making a blood smear the most direct and effective method for detecting filariae in the blood.