Asthma, COPD, and Asthma-COPD Overlap Differentiated Using Sputum Cell Count

Testing sputum culture for lung diseases
Sputum cell count, as measured by a simplified method, was able to differentiate between asthma, COPD, and asthma-COPD overlap.

This article is part of Pulmonology Advisor‘s coverage of the CHEST 2019 meeting, taking place in New Orleans, LA. Our staff will report on medical research related to asthma, COPD, critical care medicine, and more conducted by experts in the field. Check back regularly for more news from CHEST 2019.

NEW ORLEANS — Sputum cell count, as measured by a simplified method, provided data to allow differentiations between asthma, chronic obstructive pulmonary disease (COPD), and asthma-COPD overlap, according to data presented at the CHEST Annual Meeting 2019 held October 19 to 23, in New Orleans, Louisiana.

Researchers from the Shizuoka General Hospital in Japan retrospectively evaluated 195 patients between July 2015 and November 2017 who had either asthma (n=95), COPD (n=61), or asthma-COPD overlap (n=39). Patient sputum samples were treated with a mucolytic agent and then centrifuged at 500 g for 5 minutes and the precipitates were transferred to a plain glass slide. The particles were crushed with a rotary motion using another clean glass slide. The resultant material was spread evenly over the slide for staining and counting as percentages. Sputum cell counts were compared between the diseases and the relationship with clinical variables was examined. The researchers constructed a receiver operating characteristic (ROC) curve analysis to assess whether the blood eosinophil count would predict the sputum eosinophil count ≥3%.

Patients with COPD had significantly lower sputum eosinophil counts, as well as higher neutrophil counts, during the stable period compared with patients with asthma and asthma-COPD overlap (mean eosinophil and neutrophil counts: asthma, 17.4% and 78.8%, respectively; COPD, 1.8% and 95.6%, respectively; and asthma-COPD overlap, 11.8% and 84.2%, respectively). However, during the period of exacerbation, there were no differences between the 3 diseases (mean eosinophil and neutrophil counts: asthma, 15.0% and 83.3%, respectively; COPD, 4.8% and 86.4%, respectively; and asthma-COPD overlap, 17.7% and 79.9%, respectively).

There were significant correlations between sputum and blood eosinophil counts among all patients during both the stable (rho=0.492) and the exacerbation periods (rho=0.529). In addition, the ROC curve analysis demonstrated that the blood eosinophil count predicted the sputum eosinophil count 3% during the stable period (AUC, 0.75 [95% CI, 0.66-0.84]; cutoff, 235 µL; sensitivity, 75.4% and specificity, 71.3%) and during the exacerbation period (AUC, 0.80 [95% CI, 0.66-0.94]; cutoff, 351 µL; sensitivity, 61.1% and specificity, 97.1%).

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The researchers concluded that this simplified sputum cell count method may be useful in clinical practice.

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Tamura K, Shirai T, Hirai K, et al. Differentiation of asthma, COPD, and asthma-COPD overlap via a simplified sputum cell count method. Presented at: CHEST Annual Meeting 2019; October 19-23, 2019; New Orleans, LA. Abstract 464.