Some factors influencing quality of spontaneous or induced sputum for inflammatory cell analysis

To find some simple clinical factors which can predict the quality of the sputum samples obtained in a large group of asthmatic subjects.

We compared the presence of sputum productive cough in the days preceding the test, easiness in expectoration during the test, and sputum macroscopic aspect (presence of visible plugs) with the quality of slides obtained from sputum processing. We also monitored changes in the quality in patients who repeated sputum collection several times, comparing those whose first sample was adequate with those whose first sample was inadequate. We analysed 547 sputum samples obtained from 238 asthmatic patients. Sputum was processed using the whole sample method.

Patients with productive cough in the days preceding the test and easy expectoration during the test produced a higher percentage of adequate samples than those without productive cough (86% vs 76 %, p=0.01) and with difficulty in expectoration (85% vs 63%, p=0.0001). "Good" macroscopic samples were associated with better quality of slides (91% vs 38%, p=0.0001). Patients with inadequate first sample (n=40) had a higher percentage of inadequate samples (55%) in the subsequent tests than patients (n=115) with adequate first sample (8%).

Patients with increased airway secretions in the days preceding the test, easy expectoration and "good" macroscopic aspect of the sputum are more likely to produce sputum sample adequate for inflammatory cell analysis. If the first sputum sample is adequate, subsequent samples are very likely to be adequate as well. If the first sputum sample is inadequate, the quality of subsequent samples cannot be predicted, since there are similar probabilities of having adequate or inadequate samples.