Blood Group & Subgrouping

• ABO forward group (measured): your red cells tested with anti-A and anti-B reagents.
• ABO reverse group (measured, where performed): your plasma tested against known A and B red cells, to confirm the forward group.
• RhD type (measured): your red cells tested with anti-D reagents.
• Subgrouping (measured): additional typing performed by the laboratory, which may include ABO subgroups or further Rh antigens. The report names each result.

No values are calculated. Unless your report states otherwise, the test does not include a screen for unexpected red cell antibodies, which is part of hospital pre-transfusion testing.

Antigens and antibodies

Blood groups are defined by antigens, molecules on the surface of red blood cells that are inherited from your parents. In the ABO system, group A red cells carry A antigens, group B carry B antigens, group AB carry both and group O carry neither. People naturally make antibodies in their plasma against the ABO antigens they lack: someone who is group A has anti-B, someone who is group B has anti-A, group O has both and group AB has neither. This is why giving blood of the wrong ABO group can be life-threatening.

The RhD antigen

The Rh system contributes the "positive" or "negative" part of your blood group. If your red cells carry the D antigen you are RhD positive, and if they do not you are RhD negative. According to the NHS, about 85% of the UK population is RhD positive. RhD matters especially in pregnancy, where an RhD-negative mother carrying an RhD-positive baby needs specific antenatal care.

Beyond ABO and RhD

ABO and RhD are only two of many blood group systems. The International Society of Blood Transfusion maintains a registry that now lists more than 40 systems and hundreds of antigens. The Rh system alone has four other main antigens (C, c, E and e), and NHS Blood and Transplant describes your combination of these as your blood "subtype". The ABO system also has subgroups, such as A1 and A2, that react slightly differently in the laboratory. Your report will state exactly which additional typing has been performed.

How grouping is done

In the laboratory, your red cells are mixed with reagents containing anti-A, anti-B and anti-D antibodies, and the pattern of clumping (agglutination) shows which antigens are present. A reverse group, testing your plasma against known red cells, checks that the antibodies match the antigens found. Agreement between the two is an important internal check.

Your report will state your ABO group and RhD type, for example "A RhD positive", followed by any subgroup results. Unlike most blood tests, there is no reference range: the result is a category.

When results are unusual or inconclusive

• Weak or partial D: some people have altered forms of the D antigen that react weakly or inconsistently. The laboratory may report your RhD type as inconclusive or recommend further testing. This is a recognised finding, not a sign of illness.
• ABO discrepancies: occasionally the forward and reverse groups do not agree, for example because of weak subgroups or low antibody levels. The laboratory may need a repeat sample.
• Recent transfusion or transplant: a transfusion in the past few months, or a bone marrow or stem cell transplant, can make results difficult to interpret. Please tell us before booking.

Why your result cannot be used for transfusion

Before any transfusion, hospital laboratories follow British Society for Haematology guidance on pre-transfusion compatibility testing. Because a single labelling error could lead to an incompatible transfusion, many hospitals also apply a "two-sample rule", confirming a new patient's ABO group on two separately collected samples. Results from an outside laboratory are not used, however accurate they are.

Most people never need to know their blood group in daily life, because it is always checked by the hospital when it matters clinically. Some people like to know it for personal interest or family records. If you would also like to help others, NHS Blood and Transplant tells blood donors their blood group after their first donation.

Blood group is not a basis for diet, fitness or lifestyle choices, and we do not offer advice of that kind.

This test may suit

• Adults who would like to know their blood group for personal interest or records

This test is not suitable for

• Preparing for surgery, transfusion or organ donation: the hospital will carry out its own testing
• Pregnancy: blood grouping and antibody screening are part of routine NHS antenatal care, and decisions about anti-D are made by your maternity team
• Establishing parentage or family relationships
• Anyone who has had a transfusion in the past few months or a stem cell or bone marrow transplant, unless discussed with us first

Your ABO and RhD groups are inherited and do not change with age. Researchers have studied links between ABO group and the risk of some health conditions, but these are population-level associations that do not predict what will happen to an individual. Outside transfusion, pregnancy and transplantation, blood group is not used in UK practice to guide personal health decisions, and knowing it does not change any recommended screening or care.

• Fasting: not needed. Eat and drink normally.
• Timing: any time of day.
• Medicines: continue as usual. Tell us about any recent blood transfusion or transplant.
• Pregnancy: if you are pregnant, your antenatal team will arrange grouping; this test does not replace it.

Choose how your sample is taken when you book. We confirm the collection option, any collection fee and the expected turnaround time before you book.

• Juvenology Clinic, Maidstone (82 King Street, Maidstone ME14 1BH): Available.
• Partner clinic near you, anywhere in the UK: Available on request. We confirm availability for your postcode before you book.
• Postal home finger-prick kit: Ask before ordering. We offer a home kit only where the laboratory confirms this test is suitable for a finger-prick sample.

Sample: Venous blood sample (whole blood; tube type confirmed by the laboratory)

Collection notes: No fasting or timing requirements. Tell us before booking about any blood transfusion in recent months or any stem cell or bone marrow transplant. A home finger-prick kit is offered only if the laboratory confirms it can perform grouping and subgrouping on a capillary sample.

The price of this test covers laboratory analysis and the laboratory's results report. The report lists each result beside the laboratory's reference range.

Beyond the blood test: optional support, priced separately

• Personalised written interpretation report: £50
• General consultation: £50
• Results consultation (results discussion and follow-up advice): £100
• Personalised programme: from £150, after we assess whether a programme suits you

Consultations are with Marina, an NMC-registered nurse. She explains what your results show and how they relate to lifestyle. No prescription service is offered with these tests.

If a result suggests you need medical follow-up, we will recommend that you see your GP and, with your consent, can provide a letter to take with you. A blood test cannot rule out every condition. If you have symptoms, speak to your GP or NHS 111, and call 999 in an emergency.

Can a hospital use my result in an emergency?

No. Hospitals always group patients themselves before transfusion and often require two separate samples. When a patient's group is unknown in an emergency, O negative red cells are often used.

What does subgrouping mean?

It refers to typing beyond the basic ABO and RhD group. Depending on the laboratory, this may include ABO subgroups such as A1 and A2, or the Rh antigens C, c, E and e. Your report states exactly what has been tested.

Can my blood group change?

Your inherited blood group stays the same throughout life. Results can appear different temporarily after a transfusion or permanently after a stem cell or bone marrow transplant.

Is there a free way to find out my blood group?

Yes. GPs do not routinely check blood groups, but NHS Blood and Transplant tells donors their blood group after their first donation, if you are eligible to give blood.

I am RhD negative. Do I need to do anything?

Not in daily life. If you become pregnant, tell your midwife; RhD-negative pregnancies have specific routine care within the NHS.

Is interpretation included?

The price covers laboratory analysis and the laboratory's report. For most people the result is straightforward, but you can add a personalised written interpretation report (£50) or a results consultation (£100) if you would like to discuss it.

1. Blood groups. NHS. https://www.nhs.uk/conditions/blood-groups/
2. Blood types. NHS Blood and Transplant. https://www.blood.co.uk/why-give-blood/blood-types/
3. Milkins C, et al. Guidelines for pre-transfusion compatibility procedures in blood transfusion laboratories. British Committee for Standards in Haematology. Transfusion Medicine, 2013;23(1):3–35. https://doi.org/10.1111/j.1365-3148.2012.01199.x
4. Blood transfusion two sample rule. North Bristol NHS Trust, Severn Pathology. https://www.nbt.nhs.uk/severn-pathology/pathology-services/haematology/blood-transfusion/blood-transfusion-two-sample-rule
5. Red Cell Immunogenetics and Blood Group Terminology Working Party. International Society of Blood Transfusion. https://www.isbtweb.org/isbt-working-parties/rcibgt.html