Investigating sensitivity, specificity, and area under the curve of the Clinical COPD Questionnaire, COPD Assessment Test, and Modified Medical Research Council scale according to GOLD using St George’s Respiratory Questionnaire cutoff 25 (and 20) as reference

BACKGROUND In the GOLD (Global initiative for chronic Obstructive Lung Disease) strategy document, the Clinical COPD Questionnaire (CCQ), COPD Assessment Test (CAT), or modified Medical Research Council (mMRC) scale are recommended for the assessment of symptoms using the cutoff points of CCQ ≥1, CAT ≥10, and mMRC scale ≥2 to indicate symptomatic patients. The current study investigates the criterion validity of the CCQ, CAT and mMRC scale based on a reference cutoff point of St George's Respiratory Questionnaire (SGRQ) ≥25, as suggested by GOLD, following sensitivity and specificity analysis. In addition, areas under the curve (AUCs) of the CCQ, CAT, and mMRC scale were compared using two SGRQ cutoff points (≥25 and ≥20). MATERIALS AND METHODS Two data sets were used: study A, 238 patients from a pulmonary rehabilitation program; and study B, 101 patients from primary care. Receiver-operating characteristic (ROC) curves were used to assess the correspondence between the recommended cutoff points of the questionnaires. RESULTS Sensitivity, specificity, and AUC scores for cutoff point SGRQ ≥25 were: study A, 0.99, 0.43, and 0.96 for CCQ ≥1, 0.92, 0.48, and 0.89 for CAT ≥10, and 0.68, 0.91, and 0.91 for mMRC ≥2; study B, 0.87, 0.77, and 0.9 for CCQ ≥1, 0.76, 0.73, and 0.82 for CAT ≥10, and 0.21, 1, and 0.81 for mMRC ≥2. Sensitivity, specificity, and AUC scores for cutoff point SGRQ ≥20 were: study A, 0.99, 0.73, and 0.99 for CCQ ≥1, 0.91, 0.73, and 0.94 for CAT ≥10, and 0.66, 0.95, and 0.94 for mMRC ≥2; study B, 0.8, 0.89, and 0.89 for CCQ ≥1, 0.69, 0.78, and 0.8 for CAT ≥10, and 0.18, 1, and 0.81 for mMRC ≥2. CONCLUSION Based on data from these two different samples, this study showed that the suggested cutoff point for the SGRQ (≥25) did not seem to correspond well with the established cutoff points of the CCQ or CAT scales, resulting in low specificity levels. The correspondence with the mMRC scale seemed satisfactory, though not optimal. The SGRQ threshold of ≥20 corresponded slightly better than SGRQ ≥25, recently suggested by GOLD 2015, with the established cutoff points for the CCQ, CAT, and mMRC scale.