A specialized microscopic examination of a thick and thin blood sample (blood film) stained with a special dye (such as Giemsa). This aims to detect and identify microfilariae (larvae) of nematode species that cause lymphatic filariasis (such as Wuchereria bancrofti, Brugia malayi) in the bloodstream. The sample is taken at a specific time (often night) that corresponds to the cyclical activity of the parasite in the peripheral blood.