Validation and evaluation of the German version of the Systemic Lupus Activity Questionnaire (SLAQ)

Disease activity accounts for damage, overall mortality and co-morbidities in SLE and should frequently be assessed to adapt therapeutic patient management. The Systemic Lupus Activity Questionnaire (SLAQ) is a patient-reported instrument for the assessment of disease activity derived from the Systemic Lupus Erythematosus Activity Measure (SLAM) and was originally developed in English. Our aim was to validate the SLAQ in German and evaluate its use in a large cohort.

We translated and adapted the SLAQ questionnaire in German. It was applied to SLE outpatients at a tertiary centre (n=328) and compared to the SLAMnolab and other SLE outcome parameters. Internal consistency, criterion validity, inter-rater and test-retest reliability as well as construct validity were examined. Correlation, Cronbach's alpha, Mann-Whitney U-test or the Kruskal-Wallis one-way analysis of variance test were ascertained where appropriate. Levels of statistical significance were defined at 5% (p<0.05). All reported p-values are two-tailed.

The German SLAQ showed a comparable strong correlation with the SLAMnolab (r=0.632, p<0.0001) as the original version of the SLAQ and presented a good to excellent internal consistency reliability (Cronbach's alpha=0.89). Accrued damage as well as low disease activity are factors possibly influencing the score. Amongst others, scores were higher in patients with more reported flares, lower self-reported overall health, lower functional status and higher daily doses of prednisolone.

Our German version of the SLAQ shows a comparable validity as the original SLAQ and is a promising instrument to survey disease activity in clinical routine as well as in clinical and epidemiological studies. Possible interacting factors need to be considered when applying.