Adam Kay says he never paid a single medical bill in his life — until, while vacationing in the US, he got a piece of glass lodged in his finger.

His finger sprang open, spurting bright red blood in every direction.

"It was really embarrassing. It was like a little fire hose," the former obstetrician told Insider. "It looked like there'd been some sort of massacre, and the blood was coming, and I couldn't stop it bleeding."

That was the day that Kay got a glimpse of just how different the US healthcare system is from the system in his home in the UK, where medical care is taxpayer-funded.

Kay swiftly headed off to the nearest emergency room, travel-insurance card in hand, for care.

"They took my card details and my insurance details," he recalled. "That was the most important thing. And that was quite weird, because that just doesn't happen back home."

Kay, a former National Health Service worker who chronicled his time as a doctor in a bestselling book, "This Is Going to Hurt," said he took great pride in being a doctor in the NHS — what he called the "closest thing" Brits have to "a national religion."

One of the biggest differences between the UK and US health systems, he's noticed, is the pay-as-you-go, employer-bankrolled nature of many American health plans. He said the for-profit US health system undermined the idea that healthcare is a basic human right.

"The NHS was founded on the principle that it's free at the point of delivery and you're treated according to clinical need, not ability to pay — whether you live in Windsor Castle or on a bench outside Windsor Station," Kay wrote in his book. "Other systems around the world might be more efficient, but I'd drag myself out of a coma to argue that none of them is fairer."

As Brexit looms, Brits are worried about their national health system, the NHS

Kay acknowledged that it's not a perfect system. In recent years, it's been tough for the NHS to find enough doctors and nurses to go around. With Brexit on the horizon, many doctors are worried that the shortages will only get worse.

Meanwhile, the UK's Conservative Party, famous for slashing the NHS's budget in recent years, won an overwhelming majority of parliamentary seats in the country's general election on Thursday. British Prime Minister Boris Johnson, the Conservative leader, has promised to reverse course and make the national healthcare system the first priority. Even so, he's proposing to spend less than his left-wing rivals.

Despite issues of cash and people power, the NHS still tends to outperform private care systems in the US. For example, the NHS said that in November, more than 80% of patients who were rushed to the ER were admitted, transferred, or discharged within four hours. In California, the average ER patient can expect to wait more than 5 1/2 before admission. Life expectancy is also shorter in the US by more than two years.

"I feel like America's been gaslit about what the NHS is," Kay said. "I speak to hugely intelligent people over here who've just been slightly brainwashed into the idea that healthcare is rationed."

Instead, he said, it's the US system that has "got this wrong."

Adam Kay. Hollis Johnson/Insider

"You've got yourself worked up into this lunatic situation where everything's itemized and everything's become hyperinflated, because it's become a marketplace," Kay said. "I don't think that should ever play a part in medicine. They're two separate things. Do what's best, clinically."

That was not how Kay's trip to the ER went.

Money should not dictate best practices in medicine, Kay said

After the bleeding stopped, Kay was shocked when his doctor said he'd have to decide what to do based on how much he wanted to spend.

"They said, 'Normally, because it was a glass injury, we would want to X-ray it, just to make sure that nothing's got into the joint, but that will be an extra $1,500.' I'm suddenly thinking, do I really [want this X-ray]? I imagine I'll get this back from my travel insurance, but if I don't, that's a lot of money on my holiday ... And then I suddenly thought, no! If I was the doctor back home, I wouldn't suggest it as an option. I would say, 'This is best practice.'"

The cost of US healthcare has consistently been at the top of the list of issues Americans are most worried about. Healthcare bills are the most common reason Americans file for bankruptcy protection. In the UK, while people are still concerned about the direction of their national healthcare system, they're more likely to say their top life worry is a looming Brexit deal, or crime, or maybe the environment.

"You should never have to sell your house 'cause you got ill," Kay said. "You should never, ever have to say, 'I can't afford this medical treatment I need.' I've just grown up in an environment where it's effectively a human right. You get the healthcare you need."