[This blog post was updated on 28 June 2017 to include some more sources that estimate voluntary blood donation in India and to address other issues around it.]

Need a unit of A- blood delivered to your hospital? There’s an app for that.

Nature India intern Kate Telma, from the Graduate Program in Science Writing at the Massachusetts Institute of Technology (MIT), met an enthusiastic group of blood donors at the India Habitat Centre in New Delhi this week.

Here’s her guest post on this life-saving app they launched to mark World Blood Donor Day on June 14.

While cycling through the city, your phone pings. Someone in the area with your blood type needs blood. In less than a minute, you swipe through the pre-screening questions — Any drinks last night? Currently on antibiotics? Dengue, chikungunya, or jaundice in the last six months? Pre-screening approved, you head to the nearby hospital to donate blood.

That’s the ‘Donor On Call’ Android app (iOS and Windows versions in the works), which connects patients in the National Capital Region of India with nearby, voluntary blood donors.

The number of non-remunerative blood donations in India has been on the rise since the country adopted the in the early 2000s. The World Health Organization (WHO) estimated that voluntary blood donation in India had risen to 85% percent in 2016. But hematologist Dharma Choudhury, who mentors Donor On Call, estimates the percentage of voluntary donations to be much lower. The remainder of collected blood units are known as “replacements”.  When someone needs a blood transfusion, family members and friends are called to give units of blood to the hospital blood bank to replace the blood credited to the patient.

Pratap Chandnani founded Donor On Call in 2014 through the Green Shakti Foundation, an organization that engages Delhi NCR citizens on issues of environmental sustainability, urbanization, and resource utilization. By connecting recipients directly with donors in real time, Chandnani hopes to reduce blood storage costs, and to prevent wasting some of the estimated 600,000 litres of blood thrown out by hospitals across India in the last five years. Though discarding some of these blood units was inevitable—donated blood needs to be screened for sterility and pass serological testing before it can be safely given to anybody else—some of the blood was likely thrown out because it had been stored beyond its validity.

Unlike more traditional organ and blood donation programmes, Donor On Call encourages donors to get to know recipients. “Very rarely, there are situations where people want to donate on their birthday, or their anniversary,” to anybody who needs it, says Chandnani. “As a norm, it will be a specific need. You know the patient; you have an idea of the disease.”

The choice of allowing the donor to know the recipient—and vice versa—is not without controversy. Rajat Kumar Agarwal, a senior volunteer at the Sankalp India Foundation in Bangalore, cites the WHO Code of Ethics for Blood Donation and Transfusion, which mandates anonymity between donor and recipient.

“By suggesting that blood donation should happen at the time of need, [and] that too with the involvement of the family of the patient, the proposed solution actually violates two fundamental elements of the design of any modern blood transfusion service – a) The need to have adequate supply of blood on [the] shelf for each patient in need – thoroughly tested and processed. And b) the fact that the responsibility of organising blood is that of the hospital and not of the patient’s family,” Agarwal wrote in an email to Nature India.

Currently, Donor On Call is focused on building a robust donor base in the Delhi NCR area, and has roughly 6,100 donors registered so far. In addition to organizing blood for specific rare groups, Donor On Call encourages donors to pursue a healthy lifestyle through yoga, cycling, running and nature walks. Demand for the service is spreading to smaller towns such as Singrauli and Simla, but Chandnani worries that the mobile network might not support the app in the northern region. The developers are also creating a manual call-in option for people without access to smart phones.

Donors at the launch voiced some concerns, like feeling they needed to donate in response to a request, even if they couldn’t. In some cases, concerned family members submit several requests, depleting the donors in the area even without medical need. And there was a rumour of a couple rogue donors charging for their donation. Chandnani’s concerns for the app centre around seasonal impacts and climate change. Shifting weather patterns have brought previously unseen diseases such as dengue to the area. The air pollution levels during the winter in Delhi are very high, so a good number of donors go on antibiotics.