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Correspondence |

Lung Function Testing Prediction Equations Response: Do They Fit All? FREE TO VIEW

Simon Kwok Fai Leung, MPH; Wing Wai Yew, MBBS, FCCP; Poon Chuen Wong, MBBS, FCCP
Author and Funding Information

Affiliations: Tuberculosis and Chest Unit, Grantham Hospital, Hong Kong, People's Republic of China,  Queen Mary Hospital, The University of Hong Kong, Pokfulam, Hong Kong, China

Correspondence to: Simon Kwok Fai Leung, MPH, Respiratory Laboratory, Grantham Hospital, 125 Wong Chuk Hang Rd, Aberdeen, Hong Kong, People's Republic of China; e-mail: skfleung@netvigator.com



Chest. 2008;133(5):1288-1289. doi:10.1378/chest.07-2807
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Published online

The American Thoracic Society (ATS) recommends updating prediction equations of lung function testing preferably on a regular basis.1A new set of prediction equations for spirometry derived from the general population of Hong Kong was published in 2006.2 As many lung diseases chiefly affect subjects beyond middle age, use of such equations may underpredict or overpredict the “normal” lung function values in these older patients.

From January 2001 to March 2003, among 230 Chinese female patients referred from the thoracic surgical unit of our hospital to the lung function laboratory, 33 women had small solitary lung nodules (≤ 3 cm) on CT scans. After excluding those with smoking history, obesity (body mass index > 30 kg/m2), old age (> 80 years), short stature (< 145 cm), and unsatisfactory flow-volume loop maneuver, the remaining 28 women were included for data analysis. The women underwent lung function testing (SensorMedics 2200 System; SensorMedics; Yorba Linda, CA). ATS 1994 guidelines constituted the reference standard for the procedures and quality control. Percentages of predicted values of FEV1 and FVC were calculated by the new set of prediction equations of Ip et al,2and that of Knudson et al,3as the latter is currently used in our laboratory. National Health and Nutrition Examination Survey (NHANES) III reference equations, as recommended by the ATS,4 were used largely as an overprediction control for the oriental population. The means of percentage of predicted FEV1 and percentage of predicted FVC were compared with the target value (100) using one-sample t test. Data were analyzed using statistical software (SPSS version 11.5; SPSS; Chicago, IL).

The age of the 28 selected women was 57 ± 7.9 years (mean ± SD), and height was 156 ± 3.4 cm. The deviations of means of the percentage of predicted FEV1 from the target value were 9 (95% confidence interval [CI], 4 to 14), − 2 (95% CI, − 7 to 2), and − 8 (95% CI, − 13 to − 4) for the sets of equations of Ip et al,2Knudson et al,3and NHANES III,4 respectively. For percentage of predicted FVC, respective values were 10 (95% CI, 5 to 15), 2 (95% CI, − 3 to 6), and − 9 (95% CI, − 13 to − 4).

Despite the small sample of our study patients, a problem of significant underprediction using the prediction equations of Ip et al2 appears to exist, leading to means of percentage of predicted FEV1 and percentage of predicted FVC both > 100. Thus, application of this set of prediction equations may not be totally optimal in some clinical settings such as preoperative assessment for lung resections in female subjects in Hong Kong. We are planning a similar, larger scale study in patients with COPD currently to evaluate the issue further.

The authors have no conflicts of interest to disclose.

The material here presented is original and is not currently under consideration nor has been accepted for publication elsewhere. All authors have read the manuscript and approved its submission. All authors have no conflicts of interest to disclose.

Pellegrino, R, Viegi, G, Brusasco, V, et al (2005) Interpretative strategies for lung function tests.Eur Respir J26,948-968. [PubMed] [CrossRef]
 
Ip, MS, Ko, FW, Lau, AC, et al Updated spirometric reference values for adult Chinese in Hong Kong and implications on clinical utilization.Chest2006;129,384-392. [PubMed]
 
Knudson, RJ, Slatin, RC, Lebowitz, MD, et al The maximal expiratory flow-volume curve: normal standards, variability, and effects of age.Am Rev Respir Dis1976;113,587-600. [PubMed]
 
Hankinson, JL, Odencrantz, JR, Fedan, KB Spirometric reference values from a sample of the general U.S. population.Am J Respir Crit Care Med1999;159,179-187. [PubMed]
 
To the Editor:

Leung et al reported substantial differences in percentage of predicted FEV1 and percentage of predicted FVC when three prediction methods, namely Ip et al,1Knudson et al,2and the National Health and Nutrition Examination,3 were applied to a group of 28 Chinese women with solitary lung nodules. Leung et al expressed concerns about the utility of the prediction equations that were derived from the local population.1

Our predicted equations were derived by aiming at minimizing the absolute difference between the observed and the predicted values for each spirometric parameter (FEV1 and FVC), rather than that of their predicted percentages (percentage of predicted FEV1 or percentage of predicted FVC = [observed FEV1 or FVC/predicted FEV1 or FVC] × 100%). With regard to the predicted percentages, we compare the use of the three prediction equations using our original set of 595 Hong Kong women with mean age of 46 years (SD, 17 years; range, 10 to 80 years) and mean height of 155 cm (SD, 6.3; range, 133 to 183). There is no evidence of outliers, and normality assumption is checked and fulfilled. The 95% confidence intervals for percentage of predicted FEV1 using the three sets of equations of Ip et al,1Knudson et al,2and National Health and Nutrition Examination Survey3 are 98.8 to 101.2, 104.9 to 107.5, and 83.3 to 85.2, respectively, while the corresponding 95% confidence intervals for percentage of predicted FVC are 98.8 to 101.2, 84.3 to 86.4, and 58.3 to 61.1. As a result, our equations give the most accurate predicted percentages, with the corresponding confidence intervals including 100, and in effect outperform other nonlocal equations when applied to our local sample.

The reported differences seen in the sample of Leung et al of 28 women may well reflect the true lung function of their patients. Why they appeared better than predicted is unclear, but bias could be present as the patients were highly selected with the specific exclusion of body mass index > 30 kg/m2 and height < 145 cm for unstated reasons. Moreover, a check of normality and outliers for the use of a one-sample t test will be good to ensure the robustness of the reported results especially in such small sample. The above may render their conclusion dubious. Nevertheless, we still believe it is prudent and worthwhile to validate our equations using a larger independent sample of patients.

References
Ip, MS, Ko, FW, Lau, AC, et al Updated spirometric reference values for adult Chinese in Hong Kong and implications on clinical utilization.Chest2006;129,384-392. [PubMed] [CrossRef]
 
Knudson, RJ, Slatin, RC, Lebowitz, MD, et al The maximal expiratory flow-volume curve: normal standards, variability, and effects of age.Am Rev Respir Dis1976;113,587-600. [PubMed]
 
Hankinson, JL, Odencrantz, JR, Fedan, KB Spirometric reference values from a sample of the general U.S. population.Am J Respir Crit Care Med1999;159,179-187. [PubMed]
 

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References

Pellegrino, R, Viegi, G, Brusasco, V, et al (2005) Interpretative strategies for lung function tests.Eur Respir J26,948-968. [PubMed] [CrossRef]
 
Ip, MS, Ko, FW, Lau, AC, et al Updated spirometric reference values for adult Chinese in Hong Kong and implications on clinical utilization.Chest2006;129,384-392. [PubMed]
 
Knudson, RJ, Slatin, RC, Lebowitz, MD, et al The maximal expiratory flow-volume curve: normal standards, variability, and effects of age.Am Rev Respir Dis1976;113,587-600. [PubMed]
 
Hankinson, JL, Odencrantz, JR, Fedan, KB Spirometric reference values from a sample of the general U.S. population.Am J Respir Crit Care Med1999;159,179-187. [PubMed]
 
Ip, MS, Ko, FW, Lau, AC, et al Updated spirometric reference values for adult Chinese in Hong Kong and implications on clinical utilization.Chest2006;129,384-392. [PubMed] [CrossRef]
 
Knudson, RJ, Slatin, RC, Lebowitz, MD, et al The maximal expiratory flow-volume curve: normal standards, variability, and effects of age.Am Rev Respir Dis1976;113,587-600. [PubMed]
 
Hankinson, JL, Odencrantz, JR, Fedan, KB Spirometric reference values from a sample of the general U.S. population.Am J Respir Crit Care Med1999;159,179-187. [PubMed]
 
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