Influenza A subtyping (H3 / pdmH1 / H5)
Influenza A (H3, pdmH1, H5)
Last reviewed 2026-08-13
Public health significance
Subtyping is how a seasonal wave becomes a novel-influenza investigation. Unsubtypable A is itself a signal.
Specimen types
Respiratory (from Flu A-positive material)
Method
Target-specific NAA
CLIA / validation
High complexity. H5 assays often remain LDT or LRN-restricted. Document the confirmation algorithm.
Interpretation
Detected / Not detected per subtype. An A-positive that is H3/H1/H5 negative is an unsubtypable event, not a negative test.
Reflex / referral
H5 detected: immediate notification and CDC/LRN confirmation per current protocol.
Quality control
Subtype-specific positives. Watch primer/probe drift each influenza season.
Reportability
H5 and unsubtypable influenza A are immediately reportable in most states.
HL7 / ELR
Separate OBX rows: 49524-2 (H3), 55465-9 (pdmH1), 68986-9 (H5).
Sources
CDC influenza laboratory guidance; LOINC influenza A subtype family.