Validation of a screening instrument for nephrogenic systemic fibrosis

To develop and pilot test a screening tool to identify cases of nephrogenic systemic fibrosis (NSF) among patients exposed to gadolinium-containing contrast agents.

Sixty English-speaking subjects were enrolled: 10 subjects diagnosed as having NSF, 10 subjects with other fibrosing skin diseases, 20 subjects with nonfibrosing skin diseases, and 20 subjects without a skin disease. Subjects answered a questionnaire with 8 closed-ended (yes/no) questions focusing on cutaneous and musculoskeletal manifestations of NSF. The subjects were evaluated by a dermatologist for the presence of clinical signs of NSF. We compared the number of affirmative responses in the NSF group to those in the other groups, and the optimal cutoff that would differentiate groups was calculated. Discrimination, positive and negative predictive values, and internal consistency were also assessed.

Subjects in the NSF group tended to provide more affirmative answers. Using a cutoff of ≥3 affirmative responses yields a sensitivity of 90% and a specificity of 70%, with an area under the curve of 0.85, indicating good discrimination. Sensitivity analysis using modified control group or weighted scores exhibited only slightly better discriminatory power. The positive predictive value of the questionnaire ranged from 0.3% to 39.7%, and its negative predictive values ranged from 97% to >99% with the different proposed prevalence estimates. The instrument had high internal consistency.

This pilot study demonstrates that this questionnaire has both high internal consistency and good discriminatory ability. Thus, it may be used to screen populations for NSF.