Psychometric properties and validation of the Italian version of the Mainz pain staging system as a tool for pain-patients referral selection.

RATIONALE, AIMS AND OBJECTIVES: Indications are lacking on which patient to refer to pain facilities. Pain-chronicity stage and outcome prognosis may be used for such aims. The Mainz pain-staging system (MPSS) classifies pain patients in three chronicity stages that respectively require more extensive management. We explored the psychometric and validation properties of its Italian version towards its application as screening/referral tool. METHODS: I-MPSS was administered to n=120 mixed non-cancer-pain outpatients. Psychometric analyses and formal validation included: content validity, by assessing the hypothesis of an existing relationship between the I-MPSS classes and criteria derived from an operational case definition of chronic pain; construct validity, by principle component analysis (PCA); the autonomous construct of the I-MPSS was assessed by the strength of the Spearman correlation between its classes and the brief pain inventory (BPI) items; and reliability, by applying Cronbach's alpha statistics. Associations between psychosocial moderators and the I-MPSS were assessed applying χ(2) analyses. RESULTS: Quantitative and qualitative analyses showed significant differences between I-MPSS classes for health care and drug utilization; BPI item scores significantly differed between the classes; Spearman correlation between I-MPSS classes and BPI items was mostly moderate or mild. PCA and scree test identified four components accounting for 63.7% of the variance. Cronbach's alpha was 0.842. CONCLUSIONS: The I-MPSS showed satisfactory psychometric and validation properties. With adequate feasibility, it enabled the screening of mixed non-cancer-pain outpatients in three chronicity/prognostic stages. Results are sufficient to warrant its use for a subsequent impact study as a prognostic model and screening tool for referring pain patients.