Thresholds for clinical importance were established to improve interpretation of the EORTC QLQ-C30 in clinical practice and research

OBJECTIVE: To establish thresholds for clinical importance (TCIs) for the five functioning and nine symptom scales of the EORTC QLQ-C30 questionnaire.

STUDY DESIGN AND SETTING: In this diagnostic study, cancer patients with mixed diagnoses and treatments completed the EORTC QLQ-C30 and anchored the questions in each domain in terms of their clinical importance. The anchor questions, concerned limitations in daily life, need for help/care, and the worries of the patient and his/her partner/family. These questions allowed categorising patients into whether they exhibited a clinically important symptom/functional impairment for each scale, and to perform a receiver operating characteristic curve analysis in order to establish TCIs.

RESULTS: Data from 498 patients from six European countries (mean age 60.4 years, 55.2% women) were analysed. For the TCIs generated using the patient questionnaire data, the EORTC QLQ-C30 scales showed sensitivity values between 0.71 and 0.97 and specificity values between 0.62 and 0.92 (area under the curve above 0.80 for all scales).

CONCLUSION: This EORTC Quality of Life Group study provides TCIs for the functioning and symptom scales of the EORTC QLQ-C30. These TCIs can increase the interpretability of the questionnaire results and foster its use in daily clinical practice and in clinical research.