Marcus Welby, welcome to the 21st century.

If the fictional Santa Monica doctor from the early 1970s were still plying his trade today, patients would be able to find him at the touch of a smartphone application. He would listen to their woes and conduct a quick triage over the phone, deciding whether the symptoms warranted a house call, an ER visit or nothing at all.

Medicast, a start-up that launched in Miami last summer, offers exactly such an app — and a network of doctors to go with it. The tiny company, which has big plans for nationwide expansion, just opened a shop in Los Angeles earlier this month.

It is part of a growing trend in on-demand consumer services, notably exemplified by Uber, the mobile-driven taxi request service that has provoked the ire of cabdrivers around the globe.

It is also the latest frontier in the burgeoning world of telemedicine, a world in which medical test results can be transmitted over smartphones in a heartbeat and companies like Teladoc, MDLive and American Well connect patients with doctors in video conferences or over the Internet.

No house call, no charge

Unlike those companies, whose bread and butter is virtual consultation, Medicast collects only if the doctor makes a house call in the flesh. No visit, no charge.

In a nod to the calmer, kinder era of house-calling physicians it evokes, Medicast also makes its service available on the company's website. It even has an old-fashioned 800 number for the Luddites among us.

"We want to make it available to anyone, which is why we have all three options," said Sam Zebarjadi, Medicast's CEO and co-founder.

At the same time, Zebarjadi said, Medicast "is focused on the 30- to 64-year-old market — people with an affinity for technology and some interest in fitness and wellness."

The company has only five full-time employees — Zebarjadi, two other co-founders and two marketing people.

The company contracts with its doctors — 20 in Los Angeles and five in Miami so far. Zebarjadi envisions the network growing to hundreds of physicians.

The company charges $249 for a home visit; the doctor keeps $170 of it. In addition to the patient-doctor connections, Medicast provides billing and other back-office services. Monthly payment plans are also available: $39 a month entitles you to two visits a year, $75 for four.

Medicast's service is not generally covered by health insurance plans, but the doctors give patients receipts for prescription drugs that might be covered. And some insurers will count the cost of the house calls against a patient's deductible for out-of-network services.

The company says it puts all its contract doctors through rigorous background checks and trains them in the best practices of house calls.

'Concierge' medical services

People in need of medical services can consult the profiles of on-call Medicast doctors (as well as reviews from previous patients) and decide whether they want to request a consultation. If they do, they are asked to enter their credit-card information. They will get a call from one of the doctors within a couple of minutes. If the doctor decides a house call is in order, the credit card will be charged.

What Medicast offers is a form of "concierge" medicine, in which patients agree to pay out of their own pockets for quicker access and longer visits with doctors. Zebarjadi thinks the company stands to profit from the fact that many primary-care doctors are overburdened — a situation likely to be exacerbated by millions of newly insured patients coming into the health care system under the Affordable Care Act.

"With urgent-care centers crowding up and retail clinics packed to the rafters, we see big opportunity," he said.

And with annual deductibles on health plans rising as high as $5,000, "a lot of people are starting to forgo their insurance and going to a service like ours. Because they're going to pay the same out of pocket. So why pay for subpar service?"

Jeremy Williams, a Los Angeles emergency room doctor who moonlights for Medicast doing house calls, said the service is a good thing for physicians and patients.

Because there is no time limit on a Medicast house call, "the doctor can spend time with you to really ascertain what's going on," he said. "You may have a sore throat, but you're also a smoker. Maybe we can have a little conversation about smoking. Or maybe you're overweight. We can talk about that."

Other big U.S. cities on the radar

That does not happen very often in the truncated office visits of a typical medical practice, Williams said. With Medicast, "the doctor gets to practice medicine the way he really likes."

The company plans to expand on many fronts. Its app, currently compatible only with iPhones, will be available for Android devices in the near future, Zebarjadi said. The company also expects to launch in other major U.S. cities over the coming months: first in San Francisco and San Diego, then Washington, Chicago and New York.

It might face some competition in New York, where a company called Pager is already providing a similar mobile-based doctor house call service. The company, launched in early May, was co-founded by Oscar Salazar, one of the big brains behind Uber. So far, it operates only in New York City and is available only evenings and weekends. Medicast is a 24-hour service.

Pager charges $300 for a house call and $50 for a consultation with no follow-up visit.

Medicast does not seem to be a company that is likely to be put off by a little competition. Acknowledging the link between Uber and his own line of business, Zebarjadi noted that his company is starting to think about other sectors.

He also said there has been some international interest — from the United Kingdom, China, Germany and India — in the on-call physician service Medicast provides.

But Medicast's near-term priority is rolling out its service across the U.S.

"We definitely see this growing," Zebarjadi said. "We want to grow into a national on-call doctor home visit service."