Reference equation for spirometry interpretation for Eastern India.

Introduction: Spirometry measurements are interpreted by comparing with reference values for healthy individuals that have been derived from multiple regression equations from earlier studies. There are only two such studies from Eastern India, both by Chatterjee et al., one each for males and females. These are however single center and approximately two decades old studies.

Aims: (1) to formulate a new regression equation for predicting FEV1 and FVC for eastern India and (2) to compare the results to the previous two studies by Chatterjee et al.

Materials And Methods: Healthy nonsmokers were recruited through health camps under the initiative of four large hospitals of Kolkata. Predicted equations were derived for FEV1, FVC and FEV1/FVC in males and females separately using multiple linear regression, which were then compared with the older equations using Bland-Altman method.

Results: The Bland-Altman analyses show that the mean bias for females for FVC was 0.39 L (95% limits of agreement 1.32 to -0.54 L) and for FEV1 was 0.334 L (95% limits of agreement of 1.08 to -0.41 L). For males the mean bias for FEV1 was -0.141 L, (95% limits of agreement 0.88 to -1.16 L) while that for FVC was -0.112 L (95% limits of agreement 0.80 to -1.08 L).

Conclusion: New updated regression equations are needed for predicting reference values for spirometry interpretation. The regression equations proposed in this study may be considered appropriate for use in current practice for eastern India until further studies are available.