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Spirometric reference equations are typically stratified by race because of racial differences in lung function, particularly between black and white individuals, at least in part because of black individuals having a smaller thorax to leg length ratio, and thus smaller lung volumes for a given height, than white individuals.1,2 Use of race-based pulmonary function equations is especially problematic in biracial/multiracial individuals, who compose an increasing portion of the US population,3 as lung physiology may not simply be an average of their composite races; use of race in pulmonary function testing has recently been questioned.4 To our knowledge, no spirometric reference equations exist for biracial or multiracial individuals.
We assessed pulmonary function in biracial (black and white) children and compared spirometric data when children were classified as being black vs white.
We recruited biracial (black and white) children aged 8 to 19 years without lung disease. Racial/ethnic background was determined by parental or self-report. The study was approved by the University of North Carolina investigational review board; informed consent was obtained.
Spirometry was performed according to American Thoracic Society guidelines.5 Forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) were recorded as absolute and percentage of predicted values (by National Health and Nutrition Examination Survey III criteria1) with subjects classified as being white and black. Paired t testing was used to compare mean spirometric percentage of predicted values by racial classification (significant P < .05).
Seventeen children (9 male, 8 female) were enrolled at mean (SD) age 12.2 (3.6) years. When classified as being black, mean FVC and FEV1 were 111% and 110% of predicted, respectively. With reclassification as being white, FVC and FEV1 were 94% and 95% of predicted, a mean difference of 16.5 percentage points for FVC (95% confidence interval, 12.5-20.7; P < .001) and 15.5 for FEV1 (95% confidence interval, 10.4-20.6; P < .001) (Figure). No subjects met American Thoracic Society/European Respiratory Society criteria5 for obstructive disease (FEV1 < 80% of predicted) when classified as being black; 2 subjects (11.7%) met obstructive criteria with white classification.
Difference in forced expiratory volume in 1 second (FEV1) percentage of predicted value (black minus white) plotted by mean (of black and white) FEV1 percentage of predicted value for each subject.
Our data illustrate the potential inadequacy of current race-based spirometric reference equations for biracial (black and white) children, with a mean difference in the percentage of predicted values of more than 15 points for FVC and FEV1.
Our study had several limitations. Small sample size has the potential to bias results toward or away from the null.6 However, the consistency of our findings makes it unlikely that they are due to chance alone; our results are also consistent with previous studies.1,7 Allowing subject self-identification of race may also introduce potential bias. However, this method of racial identification is consistent with the majority of studies using race as a variable, including those studies used to generate spirometric reference equations.1,8
Racial classification can thus have a clinically significant effect on lung function assessment and can lead to inaccurate assignment of disease. While all factors involved in racial/ethnic differences in pulmonary function (by height) have yet to be identified, the thorax to leg length ratio has been shown to be a significant contributor.2,7,9 Use of more direct measures of thorax length, such as sitting height, may be important in the future to create more accurate, more broadly applicable, spirometric reference equations.7
The “true” percentage of predicted values for biracial and multiracial children cannot be determined at this time. Interpreting the percentage of predicted value as the midpoint of white and black values may diminish the likelihood of inaccurate disease assessment; however, this does not address potential physiologic and anatomical differences that may exist. Most important is to maintain consistency in racial assignment when performing repeated evaluations, because change in racial classification on pulmonary function testing could lead to a change in percentage of predicted values without change in absolute values and might influence management or diagnosis of disease.
Correspondence: Dr Pittman, University of North Carolina Division of Pediatric Pulmonology, 130 Mason Farm Rd CB 7217, Chapel Hill, NC 27599 (firstname.lastname@example.org).
Author Contributions: Dr Pittman had full access to all data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Pittman, Van Rie, and Davis. Acquisition of data: Pittman. Analysis and interpretation of data: Pittman and Davis. Drafting of the manuscript: Pittman. Critical revision of the manuscript for important intellectual content: Pittman, Van Rie, and Davis. Statistical analysis: Pittman and Van Rie. Obtained funding: Pittman. Study supervision: Davis.
Financial Disclosure: None.
Funding/Support: This work was supported by a University of North Carolina at Chapel Hill Medical Alumni Association grant and National Institutes of Health grants UL1RR025747 and 5 T32 HL 007106-32.
Previous Presentation: This study was previously presented as an abstract/poster at the American Thoracic Society Conference; May 19, 2009; San Diego, California.
Additional Contributions: We acknowledge the help and support of Robin Johnson, RT, and James Ronk, RT. This research was made possible by funding from the University of North Carolina at Chapel Hill Medical Alumni Association and the University of North Carolina at Chapel Hill General Clinical Research Center/Translational and Clinical Sciences Institute (National Institutes of Health grant UL1RR025747).
Pittman JE, Van Rie A, Davis SD. Spirometry in Biracial Children: How Adequate Are Race-Based Reference Equations?. Arch Pediatr Adolesc Med. 2011;165(6):573-574. doi:10.1001/archpediatrics.2011.76