Defining and validating the minimal clinically important difference for the cough severity visual analogue scale in adults with subacute cough.

BACKGROUND

Subacute cough imposes a significant burden, yet determining meaningful symptom relief remains challenging. While the cough severity visual analogue scale (VAS) is widely used, its minimal clinically important difference (MCID) is undefined for this population, limiting its utility in symptom management and clinical decision-making.

OBJECTIVES

To establish the VAS MCID in adults with subacute cough, confirm its psychometric validity, and validate its utility in predicting clinical outcomes.

METHODS

Individual patient data were analyzed from two randomized trials (N = 335) involving adults with subacute, specifically post-infectious cough (PIC). Improvement was assessed using distribution-based and anchor-based methods (anchors: cough symptom score [CSS], cough quality of life questionnaire [CQLQ], and Traditional Chinese Medicine [TCM] symptom score [TCMSS]). The derived threshold was validated against the risk of progression to chronic cough to ensure clinical relevance.

RESULTS

The VAS demonstrated high convergent validity (baseline Spearman's ρ=0.70-0.84; change score ρ=0.55-0.63) and responsiveness (Standardized Response Means >1.00). ROC analyses converged on a primary MCID of ≥ 40 mm reduction. Not achieving this threshold was associated with a significantly increased risk of progression to chronic cough (RR=2.78, 95% CI 1.75-4.41; P < 0.001). Subgroup analyses indicated that MCID estimates varied by baseline severity.

CONCLUSIONS

A ≥ 40 mm reduction serves as a clinically meaningful benchmark for symptom relief in adults with subacute cough (particularly PIC). This threshold is validated by its ability to predict a lower risk of chronicity, supporting its use in evaluating therapeutic efficacy and improving patient outcomes.