People were stepping up to donate blood for young girl whose cancer diagnosis sparked a global hunt for “some of the rarest blood in the world." Now, she is in remission.

Zainab Mughal was diagnosed with neuroblastoma, an aggressive form of cancer, when she was two. As part of her treatment she needed a series of blood transfusions.

But the search for donors proved far more difficult than usual because she is missing an antigen, called Indian B, which most people have in their red blood cells.

Any blood containing the antigen would be rejected by her body.

It meant the hunt had to be confined to a very specific population, people whose two birth parents are both 100% of Pakistani, Indian, or Iranian origin. Even within that population, only 4% of people have the unusual genetic variation, according to OneBlood, the Florida-based charity that is leading the search.

On top of that, donors needed to have type O or A blood.

It was described by OneBlood as “some of the rarest blood in the world" and, while three compatible donors were quickly found, more were needed because of the number of transfusions Mughal required in the course of her treatment.

OneBlood posted about Mughal's story on Facebook, requesting for donors to come forward, in December 2018, and in the following days, more than 25,000 people came forward, leading to over 4,000 units of blood being tested.

Zainab Mughal is in remission after a global search for blood donors (OneBlood)

Ultimately the search unearthed another two matches, completing a pool of five donors, two from the United States, two from the UK, and one from Australia.

Each of the five donated repeatedly over the course of Zainab's treatment, with the blood shipped to OneBlood so it was available for Zainab when needed.

“These five donors played a significant role in saving Zainab's life," a statement from OneBlood read.

“Over the course of her treatment, Zainab received more than a dozen blood and platelet transfusions. Doctors say it would not have been possible for her to have endured the chemotherapy, surgery, and two bone marrow transplants without the blood."

Mughal recently celebrated her fourth birthday, and is now in remission and her parents are optimistic for the future.

“For those five donors, they are surely a life saver for us," Mughal's father Raheel Mughal said.

“They have given our daughter a new life and we are very thankful to them. Our best hope is that the cancer never relapses and we're very optimistic that it will not come back. We're very much looking forward to having a very normal life."

People were excited to donate since the beginning.

People were even inspired to look into their family history.

OneBlood said Zainab's case highlights the need for a diverse blood supply.

“There are many other patients, just like Zainab who have extraordinarily rare blood needs," spokeswoman Susan Forbes said.

“Finding compatible blood for these patients comes down to genetics. The only way to find specially matched blood for these patients is to increase the diversity of the donor population."