Image credit: Bethematch.com

UPDATE: In the last 24 hours, Be the Match Registry has received tremendous support, with more than 3,600 people signing up to be potential marrow donors. On an average day, the organization says it sees 200 to 300 people register.

However the need for people to sign up, as well as donate funds to help Be the Match cover the costs of testing, remains great.

ABC News' Robin Roberts announced today that she'd been diagnosed with MDS, short for myelodysplastic syndrome, a rare blood disorder that affects the bone marrow.

In a letter to viewers, Roberts, also a breast cancer survivor, said that organ donors were vitally important. Despite this need, many people don't know they can be bone marrow donors or how easy it is to become one.

According to Be The Match - an organization that helps match marrow donors to recipients, and encourage others to volunteer - more than 10,000 U.S. patients every year are diagnosed with life-threatening diseases such as leukemia or lymphoma.

Dr. Jeffrey Chell, CEO of Be the Match, said blood cancer cases were increasing in the U.S. because successful cancer treatments, like chemotherapy, sometimes do irreparable damage to the bone marrow.

Unfortunately, because 70 percent of patients don't have matching donors in their families, they'll need an unrelated adult donor, or cells from donated umbilical cord blood, Be the Match says.

The program has more than 9.5 million potential donors and nearly 165,000 available cord blood units.

"This is a need for more donors," Chell said. " The type of matching we do is very complex and precise. … It's so important that people join the registry [and] be committed to being on that registry."

To join, a person needs to be between the ages of 18 and 60, willing to donate and meet health guidelines. To register, a health history form needs to be filled out and a swab of cheek cells needs to be performed.

To find out more about donating and sign up for a registration kit from the Be the Match Registry, click here .

"This is truly an amazing gift," not only for the recipient but to the donor, Chell said. "Donors say their lives have been transformed by this altruistic act. They think of themselves differently. Their family thinks of them differently. How many people can say they've saved someone's life?"