In a medical emergency, the first question is often: “Which blood group can be given?” Understanding blood group compatibility helps families search for donors quickly and calmly. This guide explains it simply. Always follow the advice of the doctor and the blood bank — they test and cross-match every unit before it is given.
The basics: ABO and Rh
Your blood group has two parts. The letter (A, B, AB or O) tells which markers, called antigens, are on your red blood cells. The plus or minus sign is the Rh factor — positive if the Rh (D) antigen is present, negative if it is not. Together they give the eight common groups: A+, A−, B+, B−, AB+, AB−, O+ and O−.
Red cell compatibility chart
This chart is for red blood cells, which is what most patients receive.
| Patient’s group | Can receive red cells from |
|---|---|
| O− | O− |
| O+ | O+, O− |
| A− | A−, O− |
| A+ | A+, A−, O+, O− |
| B− | B−, O− |
| B+ | B+, B−, O+, O− |
| AB− | AB−, A−, B−, O− |
| AB+ | All groups |
Universal donor and universal recipient
- O negative red cells can be given to patients of any group in an emergency, which is why O− donors are often called “universal donors”. O− is also one of the rarer groups, so O− donors are always in demand.
- AB positive patients can receive red cells from all groups, so AB+ is called the “universal recipient”.
Plasma works the other way round — AB plasma suits all patients — but the hospital will decide which component a patient needs.
Who can usually donate blood?
Exact rules are set by the blood bank, but commonly followed guidelines in India include:
- Age roughly between 18 and 65 years
- Body weight of at least 45–50 kg (depending on the volume collected)
- Healthy on the day, with normal haemoglobin, pulse and blood pressure as checked at the blood bank
- A gap between whole-blood donations — typically about three months for men and four months for women
The blood bank team will ask a few questions and do quick checks before every donation. If they say not today, it is for your safety and the patient’s.
In an emergency: a quick checklist
- Note the patient’s exact blood group, the hospital name and the number of units needed.
- Ask the hospital whether they need whole blood, red cells, platelets or plasma.
- Reach out to compatible donors in the same city first.
- Share one clear message with all the details instead of many different forwards.
- Once enough donors are found, tell everyone — so nobody travels unnecessarily.
Every donor matters
One donation can help more than one patient once it is separated into components. If you are healthy, consider becoming a regular donor — and encourage friends and family to join you.
On the Kayastha Setu app, Blood Donors shows community members who have opted in to donate, with compatible groups and donors in your city first. Post an urgent request and matching donors nearby get notified instantly. For personal emergencies, set up SOS Emergency contacts too.
“Ek boond, ek jeevan” — find matching blood donors in your city, fast.
Frequently asked questions
Which blood group is the universal donor?
O negative red cells can be given to patients of any blood group in an emergency, so O− is called the universal donor.
Which blood group can receive from all groups?
AB positive patients can receive red cells from all blood groups, so AB+ is called the universal recipient.
How often can I donate blood?
Commonly followed guidelines in India suggest a gap of about three months for men and four months for women between whole-blood donations. Your blood bank will confirm what applies to you.
Can O positive donate to A positive?
Yes. A+ patients can receive red cells from A+, A−, O+ and O− donors, after the blood bank cross-matches the unit.