Laboratory testing is the only way to confirm that infection with H5 influenza viruses has occurred and is critical for both national H5N1 surveillance activities as well as optimal clinical care in this current period when H5N1 infections remain sporadic. WHO has published recommended laboratory tests to use for confirming influenza A(H5) infectioniii and guidance on the interpretation of test resultsiv. Among these tests, polymerase chain reaction (PCR) is the most common approach used by most laboratories to confirm H5 infection.
However, testing for H5 influenza virus infections is not done routinely by many laboratories. Among laboratories that do test for H5, the levels of experience and diagnostic capacities can vary.
This document provides the necessary criteria by which WHO will accept country reported H5 positive PCR test results as "confirmed".
All countries are urged to share with WHO all H5 positive specimens/virus isolates from humans so that analyses of pandemic risk, development of H5 vaccines, development and updating of diagnostic protocols and reagents, monitoring of antiviral susceptibility patterns and other important risk assessment and response activities can proceed.

WHO criteria for accepting positive PCR test results of H5 infection in humans from national reference laboratories