The Hospital Authority has suspended the use of two batches of varicella-zoster virus test kits after it was told the tests may give false positive results due to invalid calibration.

Medical device manufacturer bioMerieux notified the authority that the tests may not give accurate results on immunity against the varicella-zoster virus, which causes chickenpox.

As a result, the authority immediately switched to other batches and affected blood samples were traced.

The authority explained that Tuen Mun Hospital, Hong Kong Children's Hospital and Kowloon West Cluster used the test kits concerned, involving 411 people.

Tuen Mun Hospital and Hong Kong Children's Hospital repeated the tests for 249 blood samples and the results were consistent.

Among the 162 samples in Kowloon West Cluster, 11 were from patients. While arrangements have been made for nine patients to repeat the test, retesting is not needed for two who have had other confirmatory tests.

The remaining 151 samples belong to hospital staff, performed for recruitment screening and post-exposure contact tracing. The hospital will contact them to repeat the tests.

If indicated, chickenpox vaccination will be arranged for staff according to infection control protocols, the authority added.

The authority asserted that it will follow up with the product manufacturer and liaise with the Department of Health on the latest developments.