No tainted blood sample would have slipped through and be used undetected because all samples would also have been put through another test using chemicals unaffected by the recall, it added.

This other test is a compulsory standard for all international blood service providers, whereas the test using the affected batches of chemicals was an optional one used as 'an additional safeguard', it said.

Chiron, the manufacturer of the chemicals - called reagents - voluntarily recalled some batches of its product last Friday.

The affected batches had, since last November, been stored in a warehouse where a freezer has been found to have an inconsistent temperature.

The warehouse was not run by Chiron.

Its spokesman Eric Althoff said: 'No reports of injury or adverse events related to the use of these implicated products have been identified.'

Read the full story in Friday's edition of The Straits Times