Filaria - blood

Last updated: Sunday, 21, May, 2006

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Item Process
Specimen

5 mL fresh blood in EDTA tube; delivered immediately to the laboratory.

For suspected Bancroftian and brugian filiariasis, blood must be collected when the patient is febrile, usually after midnight unless the patient is from the South Pacific.

For suspected loiasis daytime collection of blood is required.

The pathologist should be consulted prior to collection.

Method

Direct microscopy of fresh blood or blood filtered through a polycarbonate filter (3-5 mm) followed by lysis of red cells.

Application

Investigation of recurrent (particularly nocturnal) fever in a patient from an endemic area for Bancroftian or brugian filiariasis; investigation of possible loiasis in patient who has lived in or visited an endemic area.

Interpretation

The presence of microfilariae in blood provides a definitive diagnosis.

In obstructive disease, circulating microfilariae are absent and the diagnosis must be made on clinical criteria.

The presence of eosinophilia and positive filaria antibodies supports the diagnosis.

See Filaria antibodies - serum.                                                                        

The diagnosis of loiasis is established by finding microfilariae in the blood.

Failure to find microfilariae does not rule out the diagnosis, which is usually made on clinical grounds.

Reference

Grove DI. In: Mandell GR et al eds. Principles and Practice of Infectious Diseases. 6th ed. Churchill Livingstone 2005.

Bain BJ. Blood Cells. 3rd ed. Blackwell 2002.