Medically reviewed by Dr. Hafiz Muhammad Haseeb, M.B.B.S., F.C.P.S. (Haematology), Consultant Haematologist, Al-Nasar Lab & Diagnostic Centre. Updated September 2026.
Quick answer: A blood group test identifies your ABO group (A, B, AB or O) and your Rh factor (positive or negative). It needs no fasting and no preparation, and results are usually available the same day. The Rh factor matters most in pregnancy: an Rh negative mother carrying an Rh positive baby needs anti-D injections to protect future pregnancies.
Book a blood group test: call 0300 0341944, or arrange home sample collection across Lahore on 0309 1166944.
What do ABO and Rh actually mean?
Your red blood cells carry markers on their surface. The ABO system describes which of two particular markers you have: A, B, both (AB) or neither (O).
Your immune system makes antibodies against the markers you do not have. That is why transfusing the wrong group is dangerous: the recipient’s antibodies attack the donated cells immediately.
The Rh factor, more precisely the D antigen, is a separate marker. If you have it you are Rh positive, written with a plus sign. If you do not, you are Rh negative. Around 85 to 90 percent of people are Rh positive.
Together these give the eight common groups: A+, A-, B+, B-, AB+, AB-, O+ and O-.
Who can donate to whom?
| Your group | Can receive red cells from | Can donate red cells to |
|---|---|---|
| O negative | O negative only | Everyone. The universal red cell donor |
| O positive | O positive, O negative | All positive groups |
| A negative | A negative, O negative | A and AB groups |
| A positive | A and O, positive or negative | A positive, AB positive |
| B negative | B negative, O negative | B and AB groups |
| B positive | B and O, positive or negative | B positive, AB positive |
| AB negative | All negative groups | AB negative, AB positive |
| AB positive | Everyone. The universal recipient | AB positive only |
One practical point worth knowing: hospitals always cross match before transfusing, even when the group is known. Other blood group systems beyond ABO and Rh exist, and cross matching detects incompatibilities the group alone would miss. A blood group card is useful information, never a substitute for testing at the time.
Why does Rh negative matter in pregnancy?
This is the most clinically important thing on this page, and it is frequently misunderstood.
If an Rh negative mother carries an Rh positive baby, some of the baby’s blood can enter her circulation, usually during delivery but also with bleeding, miscarriage, termination, abdominal injury or certain procedures.
Her immune system then recognises the D antigen as foreign and makes antibodies against it. This is called sensitisation, and it is permanent.
The first pregnancy is usually unaffected, because sensitisation happens at or near the end of it. The danger is to later pregnancies. Those antibodies cross the placenta and attack the red cells of a subsequent Rh positive baby, causing anaemia that can range from mild to fatal.
The prevention is straightforward and effective: an anti-D injection. It is given routinely during pregnancy and again after delivery if the baby is Rh positive, and also after any event that could cause mixing of blood. It works by clearing the baby’s cells before the mother’s immune system can respond to them.
Two things follow from this. Every pregnant woman should know her blood group early. And an Rh negative woman should never decline anti-D on the basis that the current pregnancy is fine, because the injection protects the next one, not this one.
What is the indirect Coombs test?
It checks whether an Rh negative mother has already been sensitised, meaning antibodies are already present.
The distinction matters. If the test is negative, anti-D can prevent sensitisation. If antibodies are already there, anti-D cannot reverse it, and the pregnancy is instead monitored closely for signs of anaemia in the baby.
This is why an Rh negative woman is usually tested not just for her group but for antibodies, at intervals through the pregnancy.
When should blood group be checked?
- Early in every pregnancy, as part of routine antenatal testing. This is the most important single indication
- Before any surgery, and before childbirth
- Before donating or receiving blood
- For newborns of Rh negative mothers
- Before marriage, alongside thalassemia carrier screening, which is a far more consequential test in Pakistan than most couples realise
- For identity documents, employment, visas and driving licences
- Once in a lifetime for general knowledge, since it does not change
Can your blood group change?
No. It is determined genetically and stays the same for life. The only exceptions are after a bone marrow or stem cell transplant, and certain rare medical situations.
If you have two reports showing different groups, one of them is an error, most often from mislabelling. That is worth resolving properly rather than ignoring, and it is a good reason to have the test repeated at an accredited laboratory.
How to prepare
- No fasting and no preparation required
- A small blood sample is taken from a vein in the arm
- Results are usually available the same day
- Tell the laboratory if you have had a recent blood transfusion, as it can complicate interpretation
- Mention pregnancy, since antibody testing may be added
- Keep a record of the result. It never changes, and it is genuinely useful in an emergency
Blood group testing at Al-Nasar Lab
Al-Nasar Lab & Diagnostic Centre has provided laboratory testing in Lahore since 1996 and holds ISO 15189:2022 accreditation from the Pakistan National Accreditation Council. ABO and Rh grouping, indirect Coombs testing and complete blood count are all available, with home sample collection across Lahore and same day reports.
Blood group is commonly taken together with the rest of an antenatal panel, including hepatitis screening and iron studies, all from one sample.
Find your nearest collection centre, see our full test list, or contact us to book.
Frequently Asked Questions
Do I need to fast for a blood group test?
No. There is no preparation, and the result is usually available the same day.
Which blood group is the universal donor?
O negative for red cells, because it carries neither A, B nor D markers. AB positive is the universal recipient.
Why is Rh negative important in pregnancy?
An Rh negative mother can develop antibodies against an Rh positive baby. The first pregnancy is usually fine, but later ones are at risk unless anti-D injections are given.
Can my blood group change over time?
No. It is genetic and permanent. Conflicting reports almost always mean a labelling or testing error that should be resolved.
If I know my group, do I still need cross matching before a transfusion?
Yes, always. Other blood group systems exist beyond ABO and Rh, and cross matching detects incompatibilities that the group alone cannot.
This article is for general information and is not a substitute for medical advice. Please discuss your results with a qualified doctor.
