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Laboratory Diagnosis

The most satisfactory tests for hydatidosis currently in use are the indirect fluorescent antibody, immunoelectrophoresis, the enzyme-linked immunosorbent assay (ELISA) and the radioallergosorbent (RAST) tests. However, these tests are time-consuming and require a laboratory equipped with proper instruments and trained technicians. A new dot immunobinding assay DIA for the detection of hydatid antigen-specific antibodies (HA-DIA) has been described (Mistrello et al, 1995). Correlation with ELISA-IgG and RAST-IgE was significant. HA-DIA (ECHINOSTRIP) has been demonstrated to be of good predictive value, allowing for speedy diagnosis of hydatid disease in the doctor's office and for large scale screening of populations in developing countries, and helping to confirm the findings of epidemiological ultrasound surveys.

Overall sensitivity of tests for serum antibody detection in cystic echinococcosis (CE) remains in the range of 50-80%. In individual patients the identification of IgG subclasses may allow the diagnosis of various clinical manifestations of the disease. Extensive studies from patients with CE have shown that higher concentrations of IgG4 antibodies against E. granulosus antigen B correlate with illness, and a more or less active cyst, and to some extent provide an assessment of cyst viability.

The laboratory tests used in the diagnosis of hydatid disease formerly included the Casoni intradermal test and the Weinberg complement fixation test: these tests have been widely abandoned because of their unreliability. Intradermal tests are true positive in approximately 65% of patients at best and more accurate when hydatids are in the liver rather than in lungs, brain and other organs. The complement fixation test is reportedly positive in up to 70% of cases and remains positive for up to 2 years after surgical removal of a cyst. It is thus a somewhat unreliable indicator of residual cysts elsewhere in the body. False positives are also possible as a result of cross-reaction by infection with other parasites (e.g. Schistosoma). A slight eosinophilia above 5% is present in about 20-25% of patients with hydatid disease.

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