The growing influence of practice guidelines has increased concern for potential sources of bias. Two recent guidelines for primary immune thrombocytopenia (ITP) provided a unique opportunity for a systematic comparison of different methods of practice guideline development. One guideline (International Consensus Report [ICR]) was supported by pharmaceutical companies that produce products for ITP. The ICR panel members were selected for expertise in ITP; 16 (73%) reported associations with pharmaceutical companies. The other guideline was sponsored by the American Society of Hematology (ASH); panel members were selected for lack of conflicts and for expertise in guideline development as well as for ITP. Discrepancies were conspicuous when the guidelines addressed treatment. In contrast to the ASH guideline, the ICR gave stronger recommendations for agents manufactured by companies from which the ICR or its panel members received support. These data provide direct evidence that differences in financial support and methods of evidence evaluation can influence recommendations.
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