Processing small sputum samples: a method validation study.

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.