A Sputum Screening Test to Rule Out Pneumonia at an Early Stage With High Negative Predictive Value

Background Pneumonia is a serious and widespread cause of morbidity and mortality. At an early stage, the symptoms are similar to other respiratory disorders, and there is no single criterion standard for diagnosis. Antibiotics are used too often as a precaution. Objectives The objective of this study was to perform an assessment and clinical evaluation of a rapid sputum screening test (index test) to rule out pneumonia. Methods Leftover sputum samples (467) collected at the Department of Microbiology from November 2016 to March 2017 were blindly analyzed within 72 hours with the index test. The clinical accuracy of the test was estimated for pneumonia by comparison with the established diagnosis by independent physicians (International Classification of Diseases, 10th Revision). Hepatocyte growth factor and calprotectin were measured on random samples (80), and layman volunteers (40) were asked to perform the test on artificial samples. Results Two of 73 cases of pneumonia (community-acquired and nosocomial) showed negative results by the sputum strip test (97% sensitivity and 94% negative predictive value). The test results were highly correlated to hepatocyte growth factor and calprotectin concentrations in samples (R2 = 67% respective 39%). Importantly, all of the volunteers were able to estimate the correct positive and negative results. Conclusions The novel rapid sputum test represents a feasible tool for screening and ruling out the overwhelming majority of nonsevere respiratory infections at primary care settings, at home or when properly equipped laboratories are not available.