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Serum 25-OH vitamin D level (median with IQR) by (A) GOLD grade, (B) CAT score categories, (C) mMRC grade (<2 vs ≥2).
Abbreviations: IQR, interquartile range; GOLD, Global Initiative for Chronic Obstructive Lung Disease; COPD, chronic obstructive pulmonary disease; CAT, COPD assessment test; mMRC, modified Medical Research Council.
