Definitive diagnosis can be made by demonstrating the filariae in the blood, and hydrocele fluid. Blood collection should preferably be done at night. The fluids can be examined directly after mixing with formalin and centrifugation of the fluid. Alternatively, filters are available through which the fluid can be passed and then examined under the microscope. Serum Immunoglobulins, particularly IgE are raised in Filariasis. However, this test is non–specific and many conditions, particularly allergies can cause raised IgE. The same is true with finding a high number of eosinophils in the blood as these can be seen in many conditions. Thus, the diagnosis often rests on the clinical findings.

How is it Diagnosed?
Through B. S. Examination for microfilaria.

Clinical Manifestations of Lymphatic Filariasis
The clinical manifestations of filariasis depend upon the stage in the course of infection in the human host and the worm load (adult). The stages in the course of infection may be described as follows:

A. Stage of Invasion
The infective larva gains its entry into the human host and starts undergoing further development. Diagnosis at this stage rests on the triad of: Eosinophilia, lymphadenopathy and a positive intradermal test with the supporting evidence of history of residence in an endemic area.

B. Asymptomatic or Carrier Stage
This stage is usually with no clinical manifestation. The microfilaria (mf) carriers are usually detected by night blood examination.

C. Stage of Acute Manifestations
These comprise filarial fever, lymphangitis, lymphadenitis and lymphoedema of the various parts of the body and epididymo – orchitis in the male. It is mainly because of the infection of the lymphatic vessels (channels) by the adult worm.

D. Stage of Chronic Manifestations
The clinical manifestations comprise of elephantiasis of genitals, legs or arms, hydrocele, chyluria, etc.