Blood Types and Compatibility: A Clear Guide
Medically Reviewed by Dr. Pedro Yelamo Vera, MD
Licensed Physician No. 484814280 · Official Medical College of Bizkaia (Spain)Last reviewed: 6 October 2026
What blood types are, how to find out yours in Spain, and what compatibility actually means, explained calmly by a bilingual GP.
You don't have to figure this out alone
Dr. Pedro Yelamo Vera is an independent, bilingual GP licensed in Spain. Book a 20-minute video consultation in English or Spanish for €50, with a private electronic prescription issued under Spanish law when clinically appropriate.
Coming out of a blood test with a result like “Group: A RhD positive” raises questions in any language, and even more so if you are navigating the Spanish health system for the first time. This guide explains, calmly, what blood types are and what compatibility really means.
What blood types are
Your blood type depends on proteins (antigens) on the surface of your red blood cells, determined by the genes you inherit. The ABO system defines four groups: A, B, AB and 0. On top of that, the Rh factor is either positive or negative, giving the eight common combinations (A+, A−, B+, B−, AB+, AB−, 0+ and 0−).
How to find out your blood type in Spain
The only reliable way to know is a blood test: it cannot be deduced with certainty from your parents, although inheritance gives clues. In Spain your group is determined routinely if you donate blood (through the blood banks or the Red Cross), during pregnancy, or before surgery. You can also have the test done at a private laboratory, with or without a referral.
Compatibility: the essentials
- Universal red cell donor: 0 negative, because their red cells carry no A, B or RhD antigens.
- Universal recipient: AB positive, who can in principle receive red cells from any group.
- Pregnancy: an Rh difference between mother and baby may need monitoring; your midwife or obstetrician handles this routinely.
- Plasma, platelets and transplants: the rules change depending on the component, so the decision always rests with a medical team.
When to talk to a doctor
A GP can explain your blood test results, help you prepare for a blood group test, and assess symptoms such as persistent fatigue or paleness that sometimes call for a full blood count. This service is for urgent, non-emergency care: if you have significant bleeding, signs of shock or a serious accident, call 112 or go to the emergency department.
This information is general and does not replace a personal assessment. You can book a video consultation with a licensed GP who sees patients in English and Spanish, provided they are physically in Spain. For a broader look at testing, see our guide to routine blood tests and lab work in Spain.
Medical Citations & Sources
This content is written and reviewed by a licensed physician with reference to the following official health authorities.
