Precision in Diagnosing and Classifying COPD: Comparison of Historical Height with Current Height and Arm Span to Predict FEV1

BACKGROUND Measured reductions in lung function, as a result of COPD, use a measured current value and make comparisons to a determined 'normal' value arrived at using a regression equation based upon a patients height. Osteoporosis is a recognised co-morbidity in patients with chronic obstructive pulmonary disease (COPD) and may cause excessive height loss resulting in the 'normal' values and disease progression being under-estimated. PURPOSE The aim of the study was to examine the height variation in a cohort of COPD patients and controls over a 7-8 years period and evaluate its impact on estimates of lung function and hence COPD progression. METHODS In 1999-2002 we studied a cohort of primary care patients in Sunderland, UK with and without COPD and reexamined 104 (56 male) during 2007-2009. We calculated FEV(1)% predicted for actual and estimated height (armspan/1.03 and armspan/1.01 in males and females respectively). RESULTS In 1999-2002 the subjects were aged 62.6 ± 9.4 years, BMI was 26.4± 4.7 kg/m2, predicted FEV(1) was 59.0 ±16.0, and mean actual height was 167.3±8.9cm. The actual height changed significantly (p<0.001) by 2cms over time in both genders. Whilst the overall classifications of the cohort did not change significantly when armspan was used to determine height and hence normal lung volume, individual cases did move to a classification of higher severity. CONCLUSIONS The study suggests that current measured height may underestimate the degree of impairment of FEV(1) and hence progression of COPD. The use of height, derived from armspan, may give a more accurate measure of 'normal' lung volumes and hence the degree of impairment.