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01-12-2009 | Respiratory | Article

New model to predict positive sputum cultures in COPD


Free abstract

MedWire News: Clinical markers of chronic obstructive pulmonary disease (COPD) determined during an exacerbation of the disease predict the isolation of bacteria from the sputum, results show.

The research team developed a prediction model that includes variables of purulent sputum, lung function measurements, and body mass index (BMI) and has a predictive accuracy of approximately 90%.

If verified in other studies, the "clinical identification of the patients likely to yield bacterial sputum isolates would aid in reducing unnecessary tests and save valuable healthcare resources," report Angeliki Tsimogianni (National and Kapodistrian University of Athens, Greece) and colleagues in Respirology.

Among patients with COPD exacerbations, bacteria – typically Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pneumonia, and Enterobacteriaceae – are isolated in the sputum of a significant number of patients.

At present, sputum investigations are performed in most patients with an acute COPD exacerbation, even though the role of sputum microbiology and antibiotic management is controversial. The purpose of the present study was to identify clinical predictors of positive sputum cultures.

Overall, 94 patients with a COPD exacerbation requiring an emergency visit were prospectively enrolled in this study. Of these, sputum from 36 individuals contained bacterial pathogens.

In a multivariate regression analysis, purulent sputum, forced expiratory volume in one second (FEV1), and BMI were independent determinants of a positive sputum culture.

Using receiver-operator-optimized thresholds for these variables – purulent sputum, FEV1 <35% predicted, and BMI ≤22 kg/m2 – the researchers generated a weighted model to predict the likelihood of a positive sputum bacterial culture.

The area under the curve of the model was 0.803, and when none of the risk factors were present, 86% of sputum cultures were negative.

If sputum specimens had not been sent from these patients, investigators would have done 47% less sputum culture tests (44/94), and would have missed 17% of positive cultures (6/36). None of these missed cultures had resistant pathogens, report the investigators.

"These results will be of value to clinicians, allowing them to select which patients with COPD exacerbation need to have sputum cultures," according to Tsimogianni and colleagues.

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2009

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