Diagnosis can be difficult in patients with low levels of larvae in the blood. The diagnostic work-up is usually begun after someone develops eye worm, Calabar swellings, or unexplained elevated levels of eosinophils on blood tests after travel to an affected area. The diagnosis can be made in the following ways:
- Identification of the adult worm by a microbiologist after its removal from under the skin or eye
- Identification of an adult worm in the eye by a healthcare provider in a patient with risk factors for infection.
- Identification of the larvae on a blood smear made from blood taken from the patient between 10AM and 2PM.
- Identification of antibodies against L. loa. Unfortunately these tests cannot distinguish between active infection and a history of exposure or past infection and they are not widely available in the United States.