Processing small sputum samples: a method validation study

Abstract

Background: Eosinophilia is frequently a feature of asthma. Sputum analysis can help with the diagnosis and phenotyping of asthma. The current gold standard method is unsuitable for samples <100 mg. However, children frequently produce samples below this threshold.Aim: To compare and validate our modified, small sample (>10 mg and <100 mg) sputum processing method (which omits sample filtering), with the current gold standard. Method: Prospective study of 32 adults with severe asthma providing sputum samples of sufficient size for dual processing. Results: The median (IQR) sample weight was 211.0 (162.4–185.5) mg and 57.5 (22.0–61.6) mg for standard, and small sputum sample processing respectively. There was no statistically significant difference in the median (IQR) cell counts between Method A and B, respectively: eosinophils 3.8% (1.5–14.0) versus 4.9% (1.3–15.5); neutrophils 78.1% (46.5–92.4) versus 65.0% (48.3–86.6). Conclusion: The small sputum sample processing is feasible and reliable, and yields similar results to standard processing.