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Understanding your blood genotype has become a common question for people planning a family, exploring inherited health risks, or simply trying to make sense of a result on a laboratory report. In UK clinical language, “blood genotype” almost always refers to your haemoglobin genotype — the specific pattern of haemoglobin variants you inherited from your biological parents.
This guide explains what haemoglobin genotype means, how it differs from your blood group, what results such as AA, AS, AC and SS actually describe, how the test is performed, and when someone in the UK might consider having it done.
This article is educational only. It does not diagnose any condition, and it should not replace advice from your GP, midwife, haematologist or genetic counsellor.
A haemoglobin genotype describes the combination of haemoglobin genes you carry in your red blood cells. Haemoglobin is the protein that carries oxygen from your lungs to the rest of your body, and small inherited differences in its structure produce distinct variants.
The most common haemoglobin types measured in a UK genotype test are:
Because you inherit one haemoglobin gene from each biological parent, your genotype is written as a pair of letters — for example AA, AS, AC or SS. Each letter refers to one of the haemoglobin variants above.
A haemoglobin genotype is a stable, inherited characteristic. Barring a bone marrow transplant, it does not change during your lifetime.
This is one of the most common points of confusion, so it is worth stating clearly.
Your blood group (A, B, AB or O, together with your Rh factor) describes the sugar-based antigens on the surface of your red blood cells. It matters for blood transfusion and pregnancy compatibility.
Your haemoglobin genotype describes the protein inside your red blood cells. It matters for conditions such as sickle cell disease and thalassaemia.
The two systems are inherited independently. Someone with blood group O positive could have a haemoglobin genotype of AA, AS or almost any other combination. Knowing your blood group tells you nothing definitive about your haemoglobin genotype, and vice versa.
| Feature | Blood group | Haemoglobin genotype |
|---|---|---|
| What it describes | Surface antigens on red cells | Type of haemoglobin protein inside red cells |
| Common results | A, B, AB, O with Rh+/− | AA, AS, AC, SS, SC and others |
| Main clinical relevance | Transfusion, pregnancy compatibility | Sickle cell and related haemoglobinopathies |
| How it is measured | Blood group typing | Haemoglobin electrophoresis or HPLC |
The four genotypes most people ask about are AA, AS, AC and SS. A few less common combinations, such as SC, are also important.
An AA result means you have inherited two copies of the normal adult haemoglobin gene (HbA). You do not carry the sickle cell variant, and you cannot pass it on to your children.
Most people in the UK have an AA haemoglobin genotype.
An AS result means you have inherited one normal HbA gene and one HbS gene. This is known as sickle cell trait.
Sickle cell trait is not sickle cell disease. Most people with AS have no symptoms and lead entirely normal lives. However, they are carriers, which means they can pass the HbS gene on to their children.
Sickle cell trait becomes clinically relevant in two main situations: reproductive planning (because two carriers can have an affected child) and in rare high-stress conditions such as extreme dehydration, very high altitude or intense exertion, where individuals with sickle cell trait may benefit from clinical advice.
An AC result means you have one normal HbA gene and one haemoglobin C gene. This is haemoglobin C trait. As with sickle cell trait, most people with AC have no symptoms but are carriers who could pass the HbC gene to their children.
An SS result means you have inherited two copies of the sickle cell variant. This is sickle cell anaemia, the most common form of sickle cell disease. It is a serious inherited condition that requires long-term specialist care, and it is picked up in the UK through the newborn bloodspot screening programme and antenatal screening.
If you are being newly investigated as an adult and a result suggests SS, the interpreting laboratory and your clinician will typically arrange confirmatory testing and referral to a specialist haemoglobinopathy or sickle cell service.
Not everyone falls neatly into AA, AS, AC or SS. Other results include:
If your laboratory report shows something other than AA, AS, AC or SS, the accompanying comments will usually indicate whether follow-up or referral is recommended.
Haemoglobin variants are inherited in a pattern called autosomal recessive. In practical terms, this means:
For couples where both partners are carriers, each pregnancy carries the same statistical risk, independent of any previous pregnancies.
For two AS parents, for example, each pregnancy has approximately:
These are probabilities per pregnancy, not guarantees across a family. Two AS parents can have several unaffected children in a row and still have an affected child in a later pregnancy, and vice versa.
The word “compatibility” is used loosely online, especially in family-planning discussions. In a medical context, no two adults are categorically “compatible” or “incompatible.” What matters is the statistical inheritance risk to any children they may have together.
A more accurate way to think about it is:
Couples who fall into a higher-risk category are usually offered genetic counselling in the UK, either through the NHS Sickle Cell and Thalassaemia Screening Programme in pregnancy or through their GP. A genetic counsellor can explain the specific inheritance pattern for your combination of genotypes and discuss the options that are available.
A haemoglobin genotype test is a laboratory analysis performed on a small venous blood sample, usually taken from a vein in the arm by a phlebotomist. Two laboratory techniques are commonly used:
Haemoglobin electrophoresis separates different haemoglobin variants by placing them in an electric field. Because HbA, HbS, HbC and other variants have slightly different structures, they move at different rates and produce distinct bands or peaks. This is one of the traditional confirmatory methods for haemoglobinopathies.
HPLC is a widely used method in modern UK laboratories. It separates haemoglobin variants based on how they interact with a specialised column and produces a chromatogram showing the proportion of each haemoglobin type present. HPLC is highly accurate and is used both for adult testing and in the NHS newborn screening programme.
Some laboratories use capillary electrophoresis, a modern variant of the classic electrophoresis technique. Where the result is unclear or where a specific inherited condition is being investigated, further DNA-based genetic testing may be arranged through NHS genetics services.
A standard haemoglobin genotype test does not require fasting. If it is being taken alongside other blood tests, follow the specific preparation advice given by your provider.
Learn more about our haemoglobin genotype testing service if you would like details of how the test is performed by our clinical team.
Not reliably.
Family history can provide clues. If both of your biological parents have confirmed AA genotypes, for example, it is not possible for you to be SS. Similarly, if a sibling has been diagnosed with sickle cell disease, this affects the probability that other siblings are carriers.
However, family history alone cannot tell you your specific genotype with certainty. There are also situations, discussed frequently on online forums, where a child’s result appears inconsistent with parental genotypes; in most cases this reflects a testing error, incomplete family information, or a rare haemoglobin variant that was not fully characterised. Only a laboratory test on your own blood sample can confirm your genotype.
If you have never been tested and want to know your result, a blood-based haemoglobin analysis is the only established way to do so.
You may see the words genotype and phenotype used together. Your genotype is the underlying genetic combination you inherit (for example, AS). Your phenotype is how that genetic combination expresses itself in your body — including whether you have symptoms, what proportions of each haemoglobin type appear on a laboratory report, and how you respond to certain physiological stresses.
For most people with sickle cell trait (AS), the genotype is present but the phenotype is essentially silent under everyday conditions. For someone with SS, both the genotype and the phenotype are clinically significant.
In the UK, several groups may consider haemoglobin genotype testing:
The NHS offers antenatal screening in pregnancy and newborn bloodspot screening for babies born in England. Private testing is generally used by adults outside those pathways — for example, before conception, to inform partner testing, or for personal awareness.
If you fall into any of these groups, discussing your reasons with a clinician first can help decide whether a haemoglobin genotype test is the right investigation for you.
A haemoglobin genotype test is a laboratory analysis of a blood sample that identifies which haemoglobin variants you carry. It is used to detect conditions such as sickle cell trait, sickle cell disease and haemoglobin C trait, and it is usually reported as a two-letter combination such as AA, AS, AC or SS.
No. Blood group (A, B, AB, O with Rh factor) refers to antigens on the surface of red blood cells. Haemoglobin genotype refers to the type of haemoglobin protein inside red blood cells. They are inherited independently and measured by different tests.
There is no single “correct” genotype, but AA is the most common result and indicates two copies of normal adult haemoglobin. Carrier states such as AS and AC are also considered clinically normal in day-to-day life for the individual carrying them, although they are relevant for family planning.
No. AS is sickle cell trait, which means you carry one sickle gene but have one normal HbA gene as well. People with sickle cell trait usually have no symptoms. Sickle cell disease refers to genotypes such as SS or SC, which are managed by specialist services.
Yes. In each pregnancy, two AS parents have approximately a 25% chance of an AA child, a 50% chance of an AS child (a carrier like themselves) and a 25% chance of an SS child. These are probabilities per pregnancy, not guarantees.
Reliable haemoglobin genotype testing requires a proper venous blood sample analysed in a laboratory using electrophoresis or HPLC. Home fingerprick kits marketed for other purposes generally cannot substitute for a properly performed genotype test.
No. Barring a bone marrow transplant, your haemoglobin genotype is fixed from conception. Test results can occasionally look different after a recent blood transfusion, which is why laboratories usually recommend delaying testing for a period after transfusion.
Not usually. Private laboratories such as Swift Blood Tests offer haemoglobin genotype testing without a GP referral, though we recommend discussing significant or unexpected results with your GP or a specialist.
If you would like to explore having a haemoglobin genotype test through a private UK provider, you can find full details of our service on the genetic and genotype blood testing page. We recommend interpreting any result alongside a clinician, particularly if a family planning decision or a change in medical care may follow.
