The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

APPLICABILITY OF CAUCASIAN PREDICTION EQUATIONS FOR SPIROMETRY INTERPRETATION IN NORTH INDIAN PATIENTS

Ashutosh N. Aggarwal MD,FCCP, Dheeraj Gupta MD,FCCP, Digamber Behera MD,FCCP, Surinder K. Jindal MD,FCCP. Department of Pulmonary Medicine, Postgraduate Institute of Medical Education and Research, Chandigarh, India.

Background: This study was designed to assess the impact of applying commonly used Caucasian prediction equations for interpretation of results of spirometry performed in north Indian patients.

Methods: 14733 adult patients (8155 men and 6578 women), undergoing spirometry over a four-year period, were studied. Spirometry interpretation was performed using north Indian equations (previously derived at our center) and three sets of Caucasian equations: Knudson, Crapo and European Community for Coal and Steel (ECCS). Lower limits of normal (LLN) for FEV1, FVC and FEV1/FVC were calculated using lower 90% confidence limits derived from the regression equation being used. Spirometry results were categorized as normal record, obstructive defect and restrictive defect using American Thoracic Society guidelines. Agreement between classification of spirometry results using north Indian and other equations were calculated using the Kappa estimate, both for the entire population as well as for different categories of gender, age and height. In order to assess if the lower limits of normal (LLN) for FEV1, FVC and FEV1/FVC determined by the different prediction equations could be used interchangeably across different age and height groups, limits of agreement for each set of north Indian and Caucasian equation were calculated using Bland-Altman analysis.

RESULTS: Overall, The Crapo, Knudson and ECCS misclassified results in 25.6%, 18.5% and 11.3% subjects respectively. The corresponding Kappa estimates of agreement were best for ECCS equation and worst for Crapo equation for both men and women. The Crapo equation consistently overpredicted LLN for both FVC and FEV1 in men and women in all age and height categories. It also consistently overpredicted LLN for FEV1/FVC in men and underpredicted it in women. The Knudson equation consistently underpredicted LLN for FVC and FEV1 in short and old men, and overpredicted them in women of all age and height categories. It also consistently overpredicted LLN for FEV1/FVC in men and underpredicted it in women. The ECCS equation consistently overpredicted LLN for FVC and FEV1 for short men and most women, and underpredicted LLN for FEV1/FVC in both men and women. While the LLN for FVC obtained by north Indian equation was close to 90% of LLN obtained by Caucasian equations in men of several age and height groups, the same was not true for FEV1.

Conclusions: These findings suggest a rather poor agreement between Caucasian and north Indian predicted values. Use of Caucasian equations for spirometry interpretation should be avoided in north Indian patients.

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