Background/Purpose:

The EQ-5D, a 5-dimensional multi-attribute questionnaire, and the SF-6D, derived from the SF36, are 2 indirect utility measures widely used to calculate quality-adjusted life-years in order to assess health benefits.

Objective: 1) To assess which variables at baseline are associated with EQ-5D and SF-6D in early arthritis 2) To assess which variables at baseline are associated with substantial utility differences between EQ-5D and SF-6D.

Methods: – Patients: EQ-5D and SF-6D utility measures were assessed in 813 patients included in the French nationwide ESPOIR cohort, which enrolled early arthritis (EA) patients with ≥2 swollen joints for less than 6 months and suspicion of RA.

               – Analysis:  Determinants of EQ-5D and SF-6D at baseline were assessed by multivariate linear regression. Multivariate linear regression was used to determine which aspects of EA were independently associated with the difference between the two utility measures in patients with substantial utility difference, i.e. l SF-6D – EQ5D l >0.074 (highest minimal important difference, MID).To assess the determinants of having substantial utility difference, patients were divided into 3 categories at baseline:  l SF-6D–EQ-5D l >0.074 and SF-6D>EQ-5D, l SF-6D – EQ-5D l >0.074 and EQ-5D>SF-6D and the others corresponding to no substantial difference (reference category). Variables collected at baseline were analyzed by polytomous logistic regression, with the 3 categories as dependent variables.

Results: At baseline, mean values were 0.52±0.31 (range -0.59 to 1) for EQ-5D and 0.58±0.11 (range 0.30 to 0.92) for SF-6D. In the multivariate linear regression model, higher HAQ, pain and lower mental status (AIMS2-SF) were significant determinants of a lower EQ-5D. HAQ and AIMS2-SF-mental scores explained 41.4 and 7.9% of the variance respectively. Higher HAQ, patient global evaluation, pain, fatigue, and lower mental status were significantly associated with lower SF-6D. HAQ and AIMS2-SF-mental scores explained 49.3 and 14.5% of the variance respectively.

The majority of patients presented a substantial difference between the 2 utility values>0.074 (66.5%) (mean difference 0.064 [range -0.421;0.941]). In these patients, higher disability, lower mental status and higher CRP were associated with substantial difference between EQ-5D and SF-6D. HAQ and AIMS2-SF-mental scores explained 43.3 and 2% of the variance respectively.

In the polytomous logistic regression model, HAQ, lower mental status and higher pain were associated with substantial difference between EQ-5D and SF-6D. Lower disability was associated with the probability that EQ-5D was substantially superior than SF-6D in comparison with no substantial difference. Higher disability was associated with the probability that SF-6D was substantially superior to the EQ-5D.

Conclusion: Higher functional disability is the key element leading to substantial difference between the two utility measures in EA patients. EQ-5D and SF-6D are not interchangeable especially in patients with worse functional ability and the results of cost-utility studies using different utility instruments must not be compared.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/substantial-functional-disability-is-the-key-determinant-of-discrepancies-between-eq-5d-and-sf-6d-utility-measures-in-early-arthritis-results-from-the-espoir-cohort/