Why Thousands of Low-Income Americans 'Donate' Their Blood Plasma to For-Profit Centers The U.S. supplies 94 percent of the world's paid plasma.

 -- Every day in cities across the country, tens of thousands of people wait in line to have a needle put in their arms for up to two hours.

Instead of donating their blood plasma, these people receive payments for the time it takes to give their plasma -- the clear, straw-colored liquid part of the blood that contains special proteins -- to for-profit companies. The companies purify the plasma, turning it into life-saving drugs for immune disorders and other drugs, including those used in cancer and transplant patients.

“I donate specifically for the money because I work a minimum wage job. I work as a cashier and a stocker. I used to work as a repair technician for 14 bucks an hour, so I’m used to more than what I’m getting,” David, who donates his plasma, said.

In the U.S., most people technically donate their plasma but are paid for their time doing that.

The U.S. supplies 94 percent of the paid plasma used around the world. And nearly 80 percent of the plasma centers in the U.S. are located in America’s poorer neighborhoods.

Many of the people who frequent these centers to give their plasma are full-time workers and low-income Americans who are just unable to make ends meet.

William, who has two children and works at a Burger King in Kansas City, Missouri, says he gives his blood plasma twice a week.

“I go Fridays and Sundays. Right arm I use Friday. Other I use Sunday. I switch up every time,” William said. “It’s a 21-gauge needle, so it’s pretty thick.”

The payment they receive averages about $30 to $40, and for the companies, it is a $19.7 billion global industry.

Many foreign companies come to the U.S. to get the plasma for certain drugs instead of where they are headquartered because the laws in the U.S. are favorable for plasma donations.

“For a majority of people -- apparently -- it’s relatively safe. We really don’t know what the long-term effects because it’s a relatively new phenomenon," Dr. Roger Kobayashi, a clinical professor of immunology at UCLA, said.

According to the Plasma Protein Therapeutics Association, the frequency and volume parameters for plasma donation are approved by the FDA and have been in use for approximately fifty years.

"These regulations and guidelines are based on the best available science and are in place to protect the health of plasma donors. In just the past decade, the industry has collected more than 235,000,000 source plasma donations from dedicated donors that have treated hundreds of thousands of patients all over the world," the Plasma Protein Therapeutics Association (PPTA) said in a statement to ABC News. "Source plasma donation is safe and is highly regulated. Donors must meet criteria defined by the U.S. Food and Drug Administration and voluntary industry standards. Healthy, committed donors are the foundation of plasma-derived therapies."

Kobayashi said what was once “a simple gift of life has now evolved into a multi-national, highly profitable corporate enterprise.”

“What was once an act of altruism has now evolved into an act of necessity or desperation,” said Kobayashi.

"To guarantee a safe and adequate supply of donated source plasma, it is standard industry practice to compensate donors for the significant commitment of personal time and effort required to donate," the PPTA said in a statement. "Without voluntary compensated plasma donors, a shortage of plasma would occur and manufacturers would not have the plasma they need to produce the amount of vital, life-saving therapies that are required by individuals with severe, life-threatening, chronic disease and disorders."

Gaylord, who, like William, lives in Kansas City, has two young children and gives plasma twice a week.

“[It’s] great to save somebody else’s life. You’re actually helping somebody else out here too,” Gaylord said.

On one occasion, Gaylord said he was giving plasma because his daughter had a birthday, and he needed $7.50 to buy her a bathing suit and money for a cake. He said he doesn’t want his kids to know about him giving his plasma.

“I try to take off my bandage before I get home. They ask me, ‘What’s that?’” Gaylord said of the needle scar on his arm. “I’m like, ‘It’s just a sore.’ I kind of try to, like, cover it up and change the subject. They don’t really need to know that, you know.”

When ABC News met Gaylord, he was working two jobs and is trying to get a third job, but he said in order to do so, he would need a car.

“I would be more ‘presentable,’” Gaylord said. “Place I walk -- I won’t be sweating.”

Gaylord, who said he’s had a tough life growing up, said he doesn’t resent what other people have and just wants to have enough to take care of his family.

“[I want] a bank account to where if the kids do get sick or if something happens, we take care of it,” he said.

Gaylord said he hopes for a future where he doesn’t have to give plasma to give his daughter a smile on her birthday.

“I’m grateful for any and everything that God sends my way,” Gaylord said. “However, it’ just ain’t right. People will pass you by, whatever. They don’t know what you’re going through. There’s poverty. There’s a lot of poverty around here.”