INTRODUCTION: Diffusing capacity of lungs to Carbon Monoxide (DLCO)is used to assess the lungs ability to transfer gas from inspired air to the blood. Studies of DLCO in bronchial asthma have yielded conflicting results; decreased, normal or increased values have all been reported.

MATERIALS AND METHODS: This study was a hospital based prospective cross sectional study. Patients diagnosed as Bronchial Asthma according to GINA guidelines, who were on medications and on follow up at AJ Institute of Medical

Sciences, Mangalore were included in the study over a period of 18 months. Patients were classified based on severity of asthma and were subjected to DLCO. Severity do asthma and DLCO were compared and analysed statistically.

RESULTS: Total of 80 subjects were included in the study. 48(60%) were male and 32 female. Majority i.e, 42 (52.2%) subjects had mild asthma, 26(32.5%) had moderate and 12(15%) had severe asthma. There was significant difference in mean DLCO with respect to Severity of Asthma (P value = 0.002).Among those with mild asthma, 14.3% had increased, 85.7% had normal DLCO. Among those with moderate asthma, 65.4% had increased DLCO, 34.6% had normal DLCO and among those with severe Asthma, 66.7% had increased, 8.3% had normal and 25% had reduced. There was significant association between Severity of asthma and DLCO (p=<0.001).

CONCLUSION: There is a statistically significant association between severity of asthma and DLCO. Most of the DLCO abnormalities were seen with increasing severity of asthma. DLCO was increased in majority of moderate and severe asthmatics. Reduced DLCO was seen only in severe asthma.

Key words: DLCO, Asthma, PFT, severity of asthma, types of asthma