Standardized IOS Reference Values Define Peripheral Airway Impairment-Associated Uncontrolled Asthma Risk Across Ethnicity in Children

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Although clinically useful in identifying peripheral airway impairment (PAI), impulse oscillometry (IOS) has not received universal acceptance. This may be due to variable cutoff points, and the perception that available standardized reference values may not be clinically relevant in all populations. To establish the relationship between PAI, based on standardized IOS reference values, and uncontrolled asthma as well as interchangeability between Hispanic and white reference algorithms. IOS reference values were established for upper and lower limits of normal (>95th and <5th percentile, respectively) using published algorithms in Hispanic and white children. Values exceeding normal limits (PAI) were compared in those uncontrolled and controlled for significance of differences. Probability estimates and odds ratio of uncontrolled asthma were determined for R5, R5-R20, AX, and X5 using adjusted generalized estimating equation analyses. Intraclass correlation coefficients determined interchangeability of Hispanic and white reference algorithm values. Those with uncontrolled asthma had significantly greater PAI and a higher frequency of PAI than those well controlled (P < .05), whereas odds of uncontrolled asthma increased with increasing PAI (P < .001) for all IOS measures, particularly for X5, where odds ratios ranged from 2.70 to 11.01.There was good to excellent (>70%) agreement between Hispanic and white algorithms, except for R5-R20 (<70%). PAI, defined by IOS reference values, not central airway markers (R20), is consistently related to the risk of uncontrolled asthma. This is true whether using Hispanic or white reference algorithms. Thus, standardized reference values in children offer the clinician readily available IOS cutoff points that are clinically relevant across ethnicity.