Definitive diagnosis for loiasis requires sighting of an adult worm or detection of microfilariae in the afternoon blood. Many infected individuals (especially those not native to endemic areas) do not have detectable levels of microfilariae. If parasitological diagnosis cannot be made, patients must be diagnosed based upon clinical features (especially presence of Calabar swellings), history of exposure, marked eosinophilia, and elevated antifilarial antibody titers. In amicrofilaremic individuals, definitive diagnosis is sometimes obtained following initiation of DEC therapy (see therapy section) when adult worms begin to die and a subcutaneous biopsy of an allergic swelling at the site of death yields an adult worm.

The image was found on Jerry Mings's Medical Clip Art Page