Differences between observers in interpreting double-blind placebo-controlled food challenges: a randomized trial.

Background: Interpretation of double-blind placebo-controlled food challenges (DBPCFC) can be difficult, particularly with ambiguous subjective symptoms. Early opening of the challenge key (which day is verum and which placebo) may influence the clinician's interpretation of the DBPCFC result.

Methods: Fifty-one clinicians reviewing results of 19 DBPCFCs with ambiguous clinical symptoms were randomized into a key first strategy (opening the DBPCFC key before reviewing the symptoms on both challenge days and deciding on the DBPCFC result) or a symptoms first strategy (reviewing symptoms and interpreting both test days as positive or negative before opening the key and deciding on the DBPCFC result).