The use of induced sputum to investigate airway inflammation.

Clinicians have been interested in the macroscopic and protocol (fig 1), based on that described by Pin et al using a relatively low output ultrasonic nebuliser (output 0.9 ml/ microscopic appearance of sputum in asthma since the last half of the 19th century when Charcot-Leyden crystals, min, particle size 5.6 lm), results in successful sputum induction in 76% of normal and asthmatic subjects who Curschmann’s spirals, and their association with sputum eosinophilia was first recognised in patients with asthma. cannot produce sputum spontaneously. Cell counts and biochemical content of induced and spontaneous sputum Forty years ago Morrow Brown suggested that the microscopic examination of sputum might be clinically useful are similar with the exception of fibrinogen which is present in higher concentrations in spontaneous sputum. With by showing that the presence of eosinophils in a crude Leishman stained sputum smear identified patients whose salbutamol premedication and careful monitoring of forced expiratory volume in one second (FEV1) during sputum wheeze was responsive to corticosteroids. Recently, with the recognition that even mild asthma is associated with induction in mild asthma significant bronchoconstriction rarely occurs, but it is more common in patients with evidence of airway mucosal inflammation in bronchial biopsy specimens and bronchoalveolar lavage fluid, 4 there more severe or uncontrolled asthma. In a recent study a third of sputum inductions in patients with asthma has been renewed interest in the use of sputum to assess airway inflammation non-invasively. exacerbations who were overusing inhaled b2 agonists were complicated by a >10% fall in FEV1 which emphasises the This review describes the development over the last eight years of new and reliable techniques to assess airway need to perform the inductions carefully. We and other investigators have induced sputum in asthma using similar inflammation using sputum differential cell counts and measurement of molecular markers of inflammation in concentrations of hypertonic saline delivered by ultrasonic nebulisers with a higher output and, whilst there might be the sputum fluid phase. We review studies where these measurements have been made in normal and diseased a higher success rate, this is at the expense of increased adverse effects including mild bronchoconstriction. subjects and assess their validity, repeatability, and responsiveness. Finally we describe current, and speculate A recent preliminary report has suggested that the cellular and biochemical content of sputum induced by a high on future, applications of sputum measurements of airway inflammation in asthma in both research and clinical setoutput ultrasonic nebuliser changes with sequential inhalatings.