ProTransport-1 founders Elena Whorton and Mike Sechrist saw an unmet need, namely the timely transport of non-emergency medical patients.

Ambulance companies historically transported such patients, but their first priority was responding to 911 emergencies. As such, the patients who needed non-emergency transport to dialysis or surgeries were chronically late for such appointments.

Whorton and Sechrist, both paramedics, "knew firsthand these patients were treated as secondary and knew they could fulfill their needs while working as partners with hospitals and healthcare systems," Carly Clements, the company's marketing director, wrote in an email.

Founded in 2000, the company provides service from Sacramento through the Bay Area to Santa Clara.

ProTransport-1 has made the Inc. 5000 list three times and enjoyed an average annual growth of 50 percent, Clements said.

"That growth has been organic and due, almost exclusively, to word-of-mouth praise about our commitment to customer service," she said.

The company had 746 employees at the end of 2012. However, last winter ProTransport-1 laid off workers in a cost-cutting move. It now has 680 employees, including about 200 in Sonoma County, and is once more hiring, said Clements.

The company reported 2012 revenue at $36.6 million, a three-year increase of 43 percent.

This year's Inc. 5000 list ranks private companies according to percentage revenue growth from 2009 to 2012. To qualify, companies must be at least three years old, with 2009 revenues of at least $100,000 and 2012 revenues of at least $2 million.