Interpreting lung function data using 80% predicted and fixed thresholds misclassifies more than 20% of patients.
BACKGROUND
Differences in COPD classification have been shown in population data sets when using fifth percentiles as the lower limit of normal (LLN) vs the current GOLD (Global Initiative for Chronic Obstructive Lung Disease) guidelines of FEV(1)/FVC < 0.70 for detecting airway obstruction and an FEV(1) of 80% predicted for detecting and classifying the severity of COPD (GOLD/PP). Many lung function laboratories use 80% predicted to determine whether results are abnormal. Misclassification of the full range of lung diseases in large patient groups when using GOLD/PP criteria instead of the LLN has not been explored previously.


METHODS
We determined the discrepancy rates in pulmonary function test interpretation between the GOLD/PP and LLN methods on prebronchodilator lung function results from a large number of adult patients from the United Kingdom, New Zealand, and the United States.


RESULTS
In 11,413 patients, the GOLD/PP method misclassified 24%. Ten percent of patients who had normal lung function were falsely classified with a disease category, and 7% of patients were falsely attributed with emphysema. The GOLD/PP method gave false-positive classifications for airflow obstruction and restrictive defects to significantly more men (P < .01) and older patients (P < .0001) and also missed airflow obstruction and restrictive defects in younger patients (P < .0001).


CONCLUSIONS
Using lung function tests on their own with 80% predicted and fixed cut points to determine whether a test is abnormal could misdiagnose > 20% of patients referred for pulmonary function tests. The GOLD/PP method introduces clinically important biases in assessing disease status that could affect allocation to treatment groups. This misclassification is avoided by using the LLN based on the fifth-percentile values.
Department of Medicine, Queen Elizabeth Hospital Birmingham, 5th Floor Nuffield House, Birmingham B15 2TH, England. martin.miller@uhb.nhs.uk
Martin R
MR
Miller
Philip H
PH
Quanjer
Maureen P
MP
Swanney
Gregg
G
Ruppel
Paul L
PL
Enright
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003951:Diagnostic Errors / Q000706:statistics & numerical data*; D005260:Female; D005500:Follow-Up Studies; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D029424:Pulmonary Disease, Chronic Obstructive / Q000175:diagnosis* / Q000503:physiopathology; D012129:Respiratory Function Tests / Q000379:methods*; D012189:Retrospective Studies; D012720:Severity of Illness Index; D014797:Vital Capacity; D055815:Young Adult