There's a stunning coloured glass Dale Chihuly chandelier worth an estimated $1.2m in one of the hallways. Outside, lush green lawns spread peacefully around elegant white and glass blocks. The state-of-the-art labs are in a hurricane-proof building with huge windows, on the second floor in case of flooding, not in the usual drab basement. The Mayo Clinic in Jacksonville, Florida, has it all and offers some of the best medical care in the US. Yet in the midst of this billion-dollar 400-acre campus, Dr William Rupp, CEO, talks about the urgent need for the US to curb healthcare costs.

Waste is not just something that happens at lesser hospitals. Rupp says the Mayo, for all its reputation, can't be an ivory tower. "We live in the world. There is 30%-40% waste. It is not deliberate waste. It is things that have been done for a long time either because we have always done them that way or because something [bad] happens and we say: I'm going to make sure that never happens again."

So the clinic took a close look at hip replacements, for instance, and discovered that as soon as the patient left the operating room, the nurses replaced all his IV tubing, costing $100, and threw it away, replacing it with smaller tubes. Larger tubes were being used in the operating room for fear that the patient might need a blood transplant while in surgery. "So when was the last time we gave a blood transplant to an elective patient with a new hip?" asks Rupp. There was no record of such a thing in the four-year history of the hospital.

It's a tiny example of a huge nation-wide problem. US healthcare is the most expensive in the world – and the most wasteful. In 2009, the US spent over 17% of GDP on healthcare, according to a Commonwealth Fund study – more than any of 12 other industrialised countries, which spent between a third and two-thirds less. Various estimates suggest that between a third and half of US healthcare spending is unnecessary.

According to a study led by another leading Mayo clinic doctor, Rochester-based Dr Stephen Swensen, even if only 10% of the waste could be avoided, a massive $100bn could be saved.

Swensen's paper in the British Medical Journal last year was a direct appeal to US doctors. Structural change to the system is needed, but doctors do not have to wait, the paper said. "Physicians who order the tests, prescribe the medications, develop the treatment plans and execute the procedures are in a unique position to deliver results now."

If the supreme court strikes down the Affordable Care Act, which has been sold to the public partly as an attempt to save money, or if Mitt Romney repeals it, the US will still have to deal with health costs, Swensen told the Guardian. "They're twice that of the OECD, for poorer quality."

It's been a year since his paper was published, and Swensen admits he is disappointed that doctors have not rushed to pick up the gauntlet he threw down.

"Physicians are only paid about 15% of total healthcare spending but control 85% of it," he said. "We could do it today if we had enough moral imperative and initiative to do it.

"There is some activity in some of the specialist societies. These things take a while. It is harder for individuals working in a system to change. All that waste we talk about may be $1tn, but 40% of it is [contributing to] someone's income. It is hard to ask an individual, however altruistic, to take a voluntary cut."

Unnecessary admissions and too many scans

But if the doctor's mantra is "first, do no harm", the physicians ought to be lining up to support Swensen and colleagues. Unnecessary treatment exposes people to the risk of drug side-effects and cancer-causing ionising radiation from scans. "Unnecessary care may be directly responsible for as many as 30,000 patient deaths per year," says the paper.

The economic costs are astounding. Just seven of these unnecessary interventions cost the country $33bn to $62bn a year. They are antibiotics for colds and glue ear, avoidable hospitalisation for nursing home patients, over-frequent cervical cancer screening, inappropriate hysterectomies, unnecessary admission to hospital of patients complaining of chest pains, too many scans and inappropriate spinal fusion surgery for back pain.

The paper gives the example of expensive MRI scans for back pain lasting less than six weeks. The patient who has an MRI is 2.5 times more likely to have surgery – it picks up some sort of abnormality of the spine in 80% of patients over 40. But they will not be less disabled, more free from pain or in better health afterwards than those who were not sent down the MRI route – and they take longer to recover.

The US has nearly three times as many MRI machines per capita as other developed nations. Hospitals that invest in expensive scanners and doctors who are paid fees for each treatment have no financial interest in reducing their use.

At the Mayo's 23 hospitals in six settings, doctors are paid a salary, not a price per treatment. "There is no financial incentive to take someone's gall bladder," said Swensen.

In Jacksonville, Rupp says things have to change. "The fundamental issue in this country is that we have to change what we pay for. We pay for procedures and seeing people. We have never paid for taking care of the population. It is one of the fundamental differences between us and the British system."

US healthcare spending is 2.4 times the average of developed countries, but in the last six months of life, the costs go off the scale. "The NHS does better on end-of-life issues. We spend an awful lot of money on end of life cases. If we really worked with patients on what they want, we probably wouldn't do as much as we do," says Rupp.

But it would take a massive shift in social and cultural attitudes to persuade the public that some of the heroics at the end of life are doing nobody any favours. Rupp is a cancer specialist. "I have had many people telling me I have a living will. My first question is: 'Have you told your family?' The answer was often no. Then I ask" 'So what do you want me to do about that?'

"This is a new problem. It didn't exist for thousands of years. We just got sick and died. If there were a simple answer we would all be doing it. There are very complex social, ethical, mental issues here that we have only been grappling with for the last 30 years as the technology has allowed us to keep people alive longer."