Potential misinterpretation of infant lung function unless prospective healthy controls are studied.
SUMMARY RATIONALE: Reliable interpretation of pulmonary function tests relies on appropriate reference data, which remain very limited for infants.


OBJECTIVE
This study aimed to assess the validity of published reference equations for forced expiratory flow-volume (FEFV) data in infants when using current, commercially available equipment, and how this could impact on interpretation of results from infants with lung disease.


METHODS
The Jaeger Masterscreen BabyBody (v4.67) equipment was used to perform partial and raised volume FEFV maneuvers in healthy infants and those with cystic fibrosis (CF). Results were initially expressed as Z-scores using published reference equations. Multilevel modeling was used to calculate differences, if any, from predicted scores in healthy infants.


RESULTS
Data were available from 66 healthy full term infants on 89 test occasions; [median (range) postnatal age 49.4 (12-101) weeks. All FEFV outcomes were significantly lower than predicted, with mean (SD) Z-score differences of -0.4 (1.1) for FVC; -0.6 (1.0) for FEV(0.5); -1.0 (1.0) for FEF(25-75) and -1.4 (1.1) for V'(maxFRC). After adjustments using multilevel modeling, mean Z-scores were within 0.1 (SD approximately 1.0) predicted for all outcomes in healthy infants. Among 50 infants with CF, studied on 85 test occasions, results were "abnormal" (<-1.96 Z-scores) on 35 (41%) and 37 (45%) test occasions for FEV(0.5) and FEF(25-75), respectively, when using published equations. This fell to 24 (28%) and 20 (24%), respectively, after adjustment.


CONCLUSIONS
Dependence on published equations for interpreting FEFV data in infants may lead to misinterpretation of lung function status, which could impact adversely both in the research setting and on clinical management. Use of a contemporary control group or establishment of equipment-specific reference data is essential for meaningful interpretation of infant lung function data.
Lum
Sooky
S
Portex Unit, Respiratory Physiology and Medicine, UCL, Institute of Child Health, London, UK. s.lum@ich.ucl.ac.uk
Hoo
Ah-Fong
AF
Hulskamp
Georg
G
Wade
Angie
A
Stocks
Janet
J
D000465:Algorithms; D016022:Case-Control Studies; D003550:Cystic Fibrosis / Q000150:complications / Q000175:diagnosis*; D005260:Female; D005540:Forced Expiratory Flow Rates; D005541:Forced Expiratory Volume; D006801:Humans; D007223:Infant; D008171:Lung Diseases / Q000175:diagnosis* / Q000209:etiology; D008297:Male; D008432:Mathematical Computing; D011446:Prospective Studies; D012016:Reference Values