Hydatid (Echinococcus granulosus) - UKAS accredited test
Samples are screened with commercial ELISA. IHA is performed on ELISA positive samples.
Amongst proven cases of hydatid disease, 92% show a positive ELISA test. Sensitivity depends on cyst site: Liver 96%, pulmonary 76%, skeletal 60%, other sites vary. Brain hydatid rarely shows positive serology. Serological cross-reactions, giving rise to false positives, can occur with other parasitic infections, particularly larval cestodes, and filarial worms and with some neoplasms. Less than 3% of non-infected controls are positive.
False negatives may occur (about 8%) and are more common in patients with extra-hepatic cysts. False negatives can be due to calcified cysts. Patients with cysts occurring in the brain are usually serologically negative.
Antibody levels are detected at variable timescales post-infection due to the nature of the disease.
Antibody levels may remain positive for life post successful treatment/surgery.
IHA is performed on all samples with positive hydatid ELISA serology.
|
|
SENSITVITY % |
SPECIFICITY % |
|
ELISA (in house verification) |
100 |
97.6 |
|
IHA (manufacturers analysis) |
93 |
94.9 |
The sensitivity of the ELISA is estimated to be 97%, the cases with negative serology but subsequently proven hydatid disease have mainly been those patients with extra-hepatic lesions.
Samples found equivocal by ELISA are re-tested by IHA. We consider the results significant if both tests are positive. If the sample shows equivocal results, we would suggest repeating serology in 1 months’ time.
ELISA utilises Echinococcus species antigen and detects IgG antibodies.
IHA uses Echinococcus granulosis antigen.