Chronic rhinosinusitis: eosinophil blood reference values and decision limits and tissue count intravariability.

1. Our diagnostic laboratory reference interval for blood eosinophil counts of 0.00-0.4 x 10 9 /l is not transferrable to patients with eosinophilic chronic rhinosinusitis (CRS). 2. The blood eosinophil reference interval is not an arbiter of whether the disease is present or not and result comparison against the reference interval should be informed by clinical suspicion. A decision limit based on sensitivity and specificity of a test is more appropriate when applied to the CRS population. 3. Based on our cohort results, blood eosinophil counts ≥ 0.30x 10 9 /l in CRS should alert clinicians to the possibility of underlying non-steroidal exacerbated respiratory disease (NERD) and associated asthma. 4. Polyp tissue eosinophil counts have high intra-individual variability and depend on sampling site; these factors may potentially lead to under reporting of T2 eosinophilic status in the biopsy samples. 5. All patients with CRS should have a full blood count with the eosinophil count to diagnose CRS subtypes and inform on associated clinical traits.