Pulmonary function testing is based on comparison of measured values with predictors calculated from anthropometric data.á Height and weight are usually measured, but this is difficult in some patients.á When measurement is a problem, the most commonly used weight surrogate for predictor calculation is patient estimate while both armspan and patient estimate are common substitutes for measured height.á We have evaluated the accuracy of patients’ estimates and armspan as surrogates for height and weight measurement and the effect of their use in PFT predictor calculation.
Measurement of height, weight and armspan with recording of age, sex and diagnoses is the standard procedure in our PFT laboratory.á For a 2 month period patient estimates of height and weight were also recorded for purposes of QI . The magnitude and frequency of inaccuracies in these estimates and the characteristics of patients in whom inaccuracies occurred were determined and correlated.á Predictors were calculated using the surrogate anthropometrics and compared with those calculated using the measured height and weight.
104 patients (41 male, 63 female, age 47 ± 16 years) were evaluated.á Diagnoses included Asthma, COPD, Sarcoidosis, IPF, Sleep Apnea and normal function.á Self knowledge of height had only 13/64 inaccuracies, and all were small.á In contrast, 35/64 weight estimates were inaccurate.á Armspan estimated height inaccurately in 24/104 patients.á 50 patients knew neither their height or weight.á There was no relationship between inaccuracy and any clinical parameter.á Weight discrepencies altered the predicted values very little (< 1%) while height discrepencies (including armspan discrepencies) had a larger effect, changing the average predictor by 8%.
Patient estimate and armspan as measurement surrogates for height and weight have high frequencies but low magnitudes of inaccuracy.á Predictors calculated using them are only mildly affected, especially if the inaccuracy is in weight.á No patient characteristics are predictive of inaccuracy.
Measurement of height and weight during PFT testing should continue, but in special circumstances surrogate values can be used with the understanding that small non-predictable inaccuracies will occur.
William Marino, No Financial Disclosure Information; No Product/Research Disclosure Information