Assessing the Predictive Validity of the Gout Activity Score

The Gout Activity Score (GAS) has predictive validity, is sensitive to change, and correlates with relevant domains of the Gout Impact Scale (GIS), according to study data published in Rheumatology.

Investigators abstracted data from the Nottingham Gout Treatment Trial (phase 2), in which patients with 1 or more gout flare in the prior year were randomly assigned to receive either continued care as usual or nurse-led care for a 2-year follow-up period. GAS and GIS were calculated for each patient, with higher scores indicating worse disease activity and quality of life, respectively. GAS score calculation utilized data on the self-reported number of gout attacks in the previous 12 months, serum urate, patient-reported visual analog scale of gout severity, and the number of tophi. The calculated subscales of GIS included gout concern overall, gout medication side effects, unmet gout treatment need, well-being during attack, and gout concern during the attack. The relationship between GAS and GIS was examined using Spearman’s correlation and standardized response means (SRMs) were calculated to assess sensitivity to change. Poisson regression was performed to describe the association between GAS at baseline and the number of flares in the following 12 months.

Investigators extracted data on 517 study participants, 262 of whom were receiving usual care and 255 were receiving nurse-led care. The majority of patients (89.2%) were men and median disease duration was 9.54 years. A low positive correlation was observed between GAS and the gout concern overall and unmet gout treatment need domains of GIS (r=0.34-0.45). Female sex was associated with fewer gout flares (adjusted incident rate ratio [aIRR], 0.71; 95% CI, 0.51-1.00). In contrast, increasing GAS (aIRR, 1.34; 95% CI, 1.23-1.46), body mass index (aIRR, 1.16; 95% CI, 1.03-1.30), and age (aIRR, 1.12; 95% CI, 1.00-1.26) were each independently associated with more frequent gout flares.

In addition, patients taking anti-inflammatory drugs at the baseline visit had more flares than patients who were not. Of all outcome measures, GAS was the most responsive to change (SRM, 0.89 to -0.53). Of the GIS domains, gout concern overall had the best sensitivity to change (SRM, 1.06-0.01).

These data confirm the validity of GAS as a measure of gout activity, although further research is needed to clarify the GAS cut-offs for high, moderate, and low disease activity before use in clinical settings.

Reference

Chinchilla SP, Doherty M, Abhishek A. Gout Activity Score has predictive validity and is sensitive to change: results from the Nottingham Gout Treatment Trial (phase II) [published online February 4, 2019]. Rheumatology. doi:10.1093/rheumatology/key446