Treasurer Joe Hockey's claims that his wealthy constituents enjoyed some of the highest bulk-billing rates in the country are looking a little washed out.

Mr Hockey said last week the cost of Medicare is growing at twice the speed of the economy and that co-payments are ''certainly something that is in the mix'' for the budget.

All worked out: Joe Hockey. Credit:Louise Kennerley

''Now I want to emphasise my electorate of North Sydney has one of the highest bulk-billing rates in Australia and I have one of the wealthiest electorates in Australia,'' Mr Hockey told ABC radio. ''To me there is something wrong with that.''