Blood Group (ABO and Rh)#

Plain-language guide to blood-group testing (ABO and Rh) - when it is needed, what the results mean, and how to order through TeleTest.

Your blood group is determined by two systems: the ABO system (A, B, AB, or O) and the Rh system (positive or negative). Blood group testing is most commonly done before pregnancy, before blood donation, or for personal record-keeping.

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What this test measures#

Two separate systems are tested together:

System What it measures
ABO Whether your red blood cells have the A protein, B protein, both, or neither on their surface. There are four ABO groups: A, B, AB, and O.
Rh (Rhesus) Whether your red blood cells carry the Rh-D protein. If they do, you are Rh-positive (+). If they do not, you are Rh-negative (-).

Combined, there are eight common blood types:

ABO group Rh status Approximate frequency in Canada
O+ positive ~ 39%
A+ positive ~ 36%
B+ positive ~ 8%
AB+ positive ~ 3%
O- negative ~ 7%
A- negative ~ 6%
B- negative ~ 1.5%
AB- negative ~ 0.5%

Frequencies vary substantially by ethnic background.

Who should consider testing#

Common reasons to test your blood group:

  • Pregnancy planning or early pregnancy: ABO and Rh testing is part of every standard first-trimester blood panel. Rh-negative individuals need special monitoring and a preventive medication during and after pregnancy.
  • Before blood donation: Canadian Blood Services (and Hema-Quebec) will test you when you donate.
  • Personal record-keeping: some patients want to know their blood type before travel, surgery, or for general health records.
  • Family planning: some patients want to know their and their partner's Rh status to plan pregnancy.
  • Pre-surgery (rarely): most hospitals retype before transfusion regardless of prior records, so this is not strictly needed beforehand.

Blood group testing is not part of routine annual screening for most people - it is a one-time test that does not change.

How to prepare#

  • No fasting is required.
  • No medication adjustments.
  • A single standard blood draw is all that is needed.

How to interpret your result#

The result is straightforward: your blood group is reported as one of the eight combinations above (e.g., "A positive" or "O negative"). Once tested, your blood group does not change for the rest of your life.

Donor and recipient compatibility#

The table below summarizes ABO and Rh compatibility for red blood cell transfusion:

Blood type Can donate red cells to Can receive red cells from
O- All blood types (universal donor) O- only
O+ O+, A+, B+, AB+ O- and O+
A- A-, A+, AB-, AB+ O- and A-
A+ A+ and AB+ O-, O+, A-, A+
B- B-, B+, AB-, AB+ O- and B-
B+ B+ and AB+ O-, O+, B-, B+
AB- AB- and AB+ O-, A-, B-, AB-
AB+ AB+ only All blood types (universal recipient)

In practice, hospital blood banks test compatibility in real time before any transfusion, so this table is for general understanding rather than something patients need to memorize.

Pregnancy and Rh#

The Rh system matters most in pregnancy. If a person who is Rh-negative carries a baby who is Rh-positive (inherited from the other parent), the parent's immune system can develop antibodies against the baby's blood cells. This is uncommonly a problem in a first pregnancy but can cause serious problems for future pregnancies if not prevented.

Standard Canadian prenatal practice for Rh-negative pregnant patients:

  • Blood-group testing in the first trimester
  • An injection of a preventive medication (Rh-immune globulin) around 28 weeks of pregnancy
  • The same injection within 72 hours after delivery if the baby is Rh-positive
  • The same injection after any episode of bleeding in pregnancy, miscarriage, abortion, or amniocentesis

This medication essentially blocks the parent's immune system from forming antibodies and protects future pregnancies.

TeleTest does not currently manage prenatal care. If you are pregnant, please see your prenatal-care provider for blood-group testing, Rh management, and pregnancy monitoring.

What does an abnormal or unexpected result mean?#

I'm Rh-negative. What does that mean for me?#

By itself, Rh-negative is not a medical problem - about 15% of people in Canada are Rh-negative and live entirely normal lives. The status mainly matters in two situations:

  • Pregnancy - see the section above on prenatal management.
  • Blood transfusion - if you ever need transfused red cells, Rh-negative blood is preferred when possible. Hospital blood banks handle this automatically.
My blood group has changed from a previous test. Is that possible?#

Your blood group does not change naturally during life. Differences between two tests usually mean one of the tests had a labelling or processing error, or you had a recent transfusion of donor blood. If two of your blood-group results disagree, ask for a third confirmation test.

Very rarely, bone-marrow or stem-cell transplant can change someone's apparent blood group because the donor's blood-forming cells take over. This is uncommon and would be obvious from your medical history.

My partner and I have different Rh statuses. What does that mean if we want children?#

The combination that matters in pregnancy is:

  • Pregnant partner is Rh-negative AND
  • Other parent is Rh-positive

In that combination, the baby could be Rh-positive, and the pregnant partner's immune system might develop antibodies without preventive medication. This is well-managed with the Rh-immune globulin injection described above. If both parents are Rh-negative, the baby will be Rh-negative and there is no concern. If the pregnant partner is Rh-positive, the baby's Rh status is not clinically relevant in this way.

Do siblings have the same blood type?#

Not necessarily. Each parent passes one of two ABO alleles to each child, and one of two Rh-D alleles, so siblings can have different blood types. Parents with blood types A and B can have children of any ABO type (A, B, AB, or O).

My blood type doesn't match what one of my parents has. Did I get the wrong parent?#

Inheritance of blood type is more flexible than people assume. A child of an A and a B parent can be A, B, AB, or O depending on which alleles each parent passes on. A child of two A parents can be A or O. Apparent mismatches are usually due to standard inheritance rules and not paternity surprises.

I want to donate blood. Do I need to know my blood type first?#

No - Canadian Blood Services (or Hema-Quebec in Quebec) will test your blood type as part of your first donation. You will receive your blood type after your first donation, free of charge. There is no need to test through a private lab or TeleTest beforehand.

Why isn't blood-group testing covered as routine screening under my provincial health plan?#

Blood-group testing is covered when there is a clinical reason: pregnancy, a transfusion need, or evaluation of certain medical conditions. As a stand-alone personal-knowledge test, most provincial plans do not cover it. You can:

  • Donate blood through Canadian Blood Services or Hema-Quebec and get your type for free
  • Pay out of pocket through TeleTest's partner labs
  • Wait for a clinically indicated reason when it would be covered
What about rare blood types?#

Beyond ABO and Rh-D, there are dozens of other red-cell protein systems (Kell, Duffy, Kidd, MNS, and many more). A standard blood-group test reports only ABO and Rh-D. People who need frequent transfusions (e.g., for sickle cell disease or thalassemia) sometimes have additional "extended" red-cell typing done by their specialist team to find the safest donor units. This extended typing is not part of a routine blood-group test and is not currently offered through TeleTest.

I'm traveling internationally. Should I know my blood type?#

It is reasonable to have your blood type recorded in your personal health records before international travel, but in any medical emergency where transfusion is needed, the receiving hospital will retype your blood before giving you any blood products. So while it is useful to know, it is not essential.

Does blood type affect health, diet, or personality?#

There is no scientific evidence that blood type influences diet preferences, personality, athletic performance, or general health (the "blood-type diet" is not supported by medical evidence). Blood type does have small associations with the risk of certain conditions (for example, group O has slightly lower risk of some clotting disorders), but these associations are weak and do not change clinical recommendations.

Cost and coverage#

  • TeleTest consultation fee: out of pocket.
  • Blood-group test through Canadian Blood Services / Hema-Quebec donation: free.
  • Blood-group test through your provincial health plan: covered when there is a clinical indication (pregnancy, transfusion need, certain medical conditions). Not typically covered for personal-knowledge testing.
  • Blood-group test through TeleTest as a self-pay test: available through our partner labs.

When you go for your lab draw, ask the lab technician to confirm no "carbon copy" of your result is being sent to another clinician. Present only the TeleTest requisition.

Request a TeleTest consultation#

Last reviewed: Spring 2026. Reviewed by Dr. Mohan Pandit, Chief Medical Officer at TeleTest. We review this page periodically as medical guidelines, lab practices, and provincial programs evolve. This page is for general information, not personal medical advice. If you've noticed information that may be out of date or have suggestions, please contact us - we appreciate the help keeping these resources accurate.

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