Types of Sickle Cell Disease: HbSS, HbSC, Beta-Thalassaemia
"Sickle cell" isn't one single condition. Sickle cell disease is a group of inherited blood disorders, and the type you have depends on which two haemoglobin genes you inherited. All types involve at least one S (sickle) gene. What changes is the second gene, and that affects how much healthy haemoglobin your body can make and, often, how severe things tend to be (NHLBI).
Your type is usually confirmed with a blood test such as haemoglobin electrophoresis or HPLC, often after newborn screening (WHO). If you're not sure which type you have, ask your haematology team. It's on your records and it affects your care.
HbSS: sickle cell anaemia
Genes: S from both parents. This is the most common form of sickle cell disease and is usually the most severe. With no normal beta-globin gene, nearly all of the haemoglobin is haemoglobin S. People with HbSS tend to have lower haemoglobin levels, more frequent pain crises and a higher risk of complications such as stroke and acute chest syndrome, although it varies a lot from person to person.
HbSC disease
Genes: S from one parent, C from the other. HbSC is the second most common type. It's often described as milder than HbSS, with higher haemoglobin levels and fewer crises for many people. But "milder" doesn't mean harmless. People with HbSC still get pain crises, and some complications, especially eye problems (retinopathy), can be more common than in HbSS. Regular eye checks are important.
HbS beta-thalassaemia
Genes: S from one parent, beta-thalassaemia from the other. Beta-thalassaemia genes make little or no normal beta-globin. There are two main kinds:
- HbS beta-zero (β⁰) thalassaemia. The thalassaemia gene makes no normal beta-globin, so this type usually behaves much like HbSS and is often just as severe.
- HbS beta-plus (β⁺) thalassaemia. The thalassaemia gene makes some normal beta-globin, so this type is often milder, though again it varies.
Because standard "genotype" tests don't always pick up beta-thalassaemia trait, couples planning a family should ask for a full haemoglobinopathy screen (see our genotype compatibility guide).
Rarer types: HbSD, HbSE and HbSO-Arab
Genes: S from one parent and D, E or O-Arab haemoglobin from the other. These are less common. HbSD-Punjab and HbSO-Arab can be as severe as HbSS, while HbSE is often milder. If you have one of these types, your haematologist will explain what to expect for you specifically.
Types at a glance
| Type | Genes | Typical severity* |
|---|---|---|
| HbSS (sickle cell anaemia) | S + S | Usually most severe |
| HbS β⁰ thalassaemia | S + β⁰ | Usually severe, similar to HbSS |
| HbSD-Punjab, HbSO-Arab | S + D / O-Arab | Can be severe |
| HbSC | S + C | Often milder, but eye problems more common |
| HbS β⁺ thalassaemia | S + β⁺ | Often milder |
| HbSE | S + E | Usually mild |
*Severity varies a lot between people with the same type. Your own history matters more than the label.
Is sickle cell trait a type of sickle cell disease?
No. Sickle cell trait (AS) means you have one S gene and one usual A gene. You're a carrier, not someone with the disease, and you can't develop it. See sickle cell trait vs sickle cell disease.
Why does your type matter?
- Treatment. Some treatments and trials are only approved for certain types. For example, NHS access to the Casgevy gene therapy is limited to people with HbSS, HbS β⁰ or HbS β⁺ thalassaemia (NICE).
- Monitoring. Your team may check some things more closely depending on your type, such as eyes in HbSC.
- Family planning. Your genes decide what you can pass on. Our free checker shows the chances.
See the chances for each child from two parents' genotypes.
Frequently asked questions
This guide is general information, not medical advice. Always follow the plan agreed with your own care team. Read our medical disclaimer.
Related guides
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