The Discriminatory Ability of the Fibromyalgia Rapid Screening Tool (FiRST): An International Study in Spain and Four Latin American Countries.

OBJECTIVE To assess the transcultural equivalency of the Spanish version of the Fibromyalgia Rapid Screening Tool (FiRST) and its discriminatory ability in different Latin American samples. DESIGN Validation study. SETTING Departments of Rheumatology in general hospitals and private centers; fibromyalgia unit in a university hospital. SUBJECTS 350 chronic pain patients from Spain, Argentina, Mexico, Peru, and Ecuador. METHODS The cultural relevance of the Spanish version of the FiRST was evaluated. The ability of the FiRST as a screening tool for fibromyalgia was assessed by logistic regression analysis. To determine the degree to which potential confounders, such as differences in demographics, pain, affective distress, catastrophizing, and disability, might affect the discriminatory ability, the tool was reassessed by hierarchical multivariate logistic regression. RESULTS Slightly different versions of the FiRST were recommended for use in each Latin American subsample. The FiRST showed acceptable criterion validity and was able to discriminate between fibromyalgia and non-fibromyalgia patients even after controlling for the effect of potential confounders. However, low specificities were observed in samples from Spain and Mexico. CONCLUSIONS The Spanish version of the FiRST may be used as a screening tool for fibromyalgia in several Latin American subsamples, even in those patients with high scores on potential confounders. In Spain and Mexico, the low specificity of the FiRST suggests, however, that it would be best used to support a suspected diagnosis of fibromyalgia, rather than to exclude the diagnosis.