The conclusions reached by critics of the measurement of sputum eosinophils (and other cell indices), which Dr Peters1 conveys, misrepresent the facts and are destructive to progress in the assessment and management of severe asthma, which is the focus of this debate. Although severe asthma comprises a minority of patients with asthma, it accounts for a major part of the morbidity and economic burden.
The main criticism is that the procedure is difficult, time consuming, and expensive. This perception results from a failure to recognize what is required to establish a clinical service. Sputum induction is a pulmonary function laboratory procedure, is easy to do, and takes up to 45 min. Sputum processing and examination is a medical laboratory test and, like other such tests, requires a certified technologist (who, in this instance, is trained in cell morphology) (Table 1). To such a person, the test is not difficult, it takes 1 h of time, and their salary is the chief expense. Hence, one technologist can handle eight or more tests per day. Obtaining a cell count in sputum is no different from obtaining a cell differential in other body fluids such as BAL or cerebrospinal fluid, which is widely done yet without criticism. The only improvements that we have suggested concern additional processing of sputum. This surely can be obtained in any clinical laboratory in any part of the world.