Stem cells, the precursors to other kinds of cells in the human body, promise near-miracle medical treatments such as regenerating organs or repairing nerves.

But stem cell medicine is still in the early stages. Culturing the right kind of cell remains difficult and so far only a few procedures are FDA-approved. Odds are it will be several years before a wide range of ailments can be treated with stem cells.

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For those who want to be ready for that day, some companies in the United States are offering people a chance to bank their stem cells for future use. That way when treatments are available, there will be stem cells ready to go that came from the patient's own body, eliminating the issue of rejection of donor cells. Meanwhile, the cells are presumably healthier, as they would have been collected from a younger, disease-free patient.

"With all these amazing advancements in the last few years, there will be stem cell therapies," said Vin Singh, founder and CEO of Grand Forks, N.D.-based Next Healthcare, which offers stem cell banking.

Next Healthcare is not the only bank out there. Other consumer stem cell banks – which differ from the banks used by scientific institutions -- include Biolife Cell Bank of Dallas, NeoStem Inc., of New York, BioEden of Austin, LifeBank of Burnaby, British Columbia. There are many more: stem cell banking was a $435 million business in 2012, according to a report from IBISWorld.

Stem cells can become any kind of cell in the body; they are generalists. In the womb, embryonic stem cells turn into the cells that make up the organs, nerves, blood and bone. After birth, these cells exist in a person's body as so-called adult stem cells and can be found in all kinds of tissue as they play an important role in repair.

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Certain medical therapies make use of a stem cell's unique ability to transform into other cells. For example, stem cells from umbilical cord blood are used to create healthy blood cells in order to treat certain forms of leukemia and stem cells collected from a patient's cornea are used in some types of corneal transplants. Doctors have used patients' own stem cells to partially rebuild tracheas.

To bank the stem cells, a person visits a doctor's office, where tissue samples are taken. Stem cells can theoretically come from anywhere, but usually a physician will take a small square of skin, a blood sample, a piece of fat via liposuction or even bone marrow. Some companies offer to bank stem cells from children's teeth as they lose them, and many places offer banking blood from the umbilical cords of newborns.

Certain medical therapies make use of a stem cell's unique ability to transform into other cells.Andrew Brookes/Corbis

The cells are sent to a facility where they are examined for any contamination or infection, and if nothing shows up they are put in cold storage. When they are needed, the cells are taken out and cultured into the desired cell and used for the therapy.

Some experts, however, question how useful such banks are and whether they are worth the money. Storing stem cells can cost hundreds of dollars per year and thousands of dollars over time. Next Health Care, for instance, charges $2,800 up front and $200 per year after that.

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And banking one's stem cells may be pointless when advances in biotechnology are making it possible to turn any cell from the body, such as skin, into a stem cell. The results are called induced pluripotent stem cells, or IPS. Although that process is expensive -- it can easily hit hundreds of thousands of dollars -- the cost will likely drop, said Richard Gronostajski, a professor of biochemistry and director of the University at Buffalo's Western New York Stem Cell Culture and Analysis Center. If it gets down to the thousands of dollars, then the stem cell banks would become obsolete.

Another issue is whether being younger and healthier makes any difference. Gronostajski said studies don't seem to show that it does. "We've had IPS stem cell lines made from people in their sixties and seventies. There hasn't been a significant decline from [stem cells] made from skin cells in older donors."

IPS also has one other advantage: it makes an essentially inexhaustible supply of stem cells. There's no need to bank them if it's possible to build innumerable cells on the fly and from scratch, as it were.

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John Carbona, CEO of BioLife Cell Bank of Dallas, said while it's true that obsolescence is a possibility, the high cost of IPS means that banking will likely remain the best option for most people in the short term. He said that IPS was expensive largely because it hasn't been scaled up to an industrial process. He thinks the odds are good that stem cell therapies will be available before IPS becomes cheap and easy.

"We're basically hoping that the science catches up with our bank," Carbona said.