Figures obtained under Freedom of Information rules show 35% of 5,548 GP referrals received by a referral management centre commissioned by NHS Vale of York CCG in 2013/14 were returned to practices.
The Referral Support Service sent back 14.4% of referrals because they lacked certain information or attachments, while in 12.5% of cases GPs were told to treat the patient in primary care instead.
The finding emerged as part of a wider GP investigation into the rise of referral management centres under CCGs.