Understanding the Types of Sickle Cell Disease: A Guide to SCD Genotypes

If you or someone you love lives with sickle cell disease (SCD), you may have heard terms like "HbSS," "HbSC," or "sickle cell trait" tossed around at clinic visits without much explanation. These labels aren't just medical jargon — they describe different genotypes of SCD, and the specific genotype can shape everything from how often pain crises occur to which complications a care team watches for most closely.

This guide walks through the major types of sickle cell disease in plain language, so you can better understand your own diagnosis (or a loved one's) and ask more informed questions at your next hematology appointment.

A quick refresher: what makes a genotype "sickle cell disease"?

Hemoglobin is the protein in red blood cells that carries oxygen. Sickle cell disease happens when a person inherits a gene for sickle hemoglobin (HbS) from both parents, or inherits one HbS gene along with a gene for a different abnormal hemoglobin (such as hemoglobin C, D, E, or O) or a beta thalassemia gene. The specific combination a person inherits is their genotype, and it's typically confirmed through newborn screening or hemoglobin electrophoresis.

It's worth separating this clearly from sickle cell trait (HbAS), which is inheriting one HbS gene and one normal hemoglobin A gene. Sickle cell trait is a carrier state, not a form of the disease itself, and according to the Cleveland Clinic, people with the trait usually have no symptoms, though it can occasionally matter under extreme physical stress such as dehydration or intense exertion.

The main types of sickle cell disease

HbSS — sickle cell anemia

HbSS is the most common and, per the CDC, generally the most severe form of SCD. It occurs when a person inherits two HbS genes, one from each parent. People with HbSS tend to have the lowest baseline hemoglobin levels among the SCD genotypes and often experience the disease's hallmark complications — pain crises, acute chest syndrome, and chronic anemia — more frequently than other genotypes.

HbSC disease

HbSC results from inheriting one HbS gene and one hemoglobin C gene. It's the second most common form of SCD and is generally milder than HbSS, with hemoglobin levels that are often closer to normal. There's an important exception, though: research comparing the two genotypes has found that retinopathy (damage to the blood vessels in the retina) is actually more common in HbSC than in HbSS, which is why regular eye exams matter for this group specifically. We cover HbSC in much more depth in our dedicated HbSC guide.

HbS beta thalassemia (HbSβ⁰ and HbSβ⁺)

This genotype combines one HbS gene with one beta thalassemia gene, and it splits into two meaningfully different subtypes:

• HbSβ⁰ (beta-zero): The beta thalassemia gene produces no normal hemoglobin A at all. Clinically, this subtype behaves very similarly to HbSS, according to the Merck Manual.
• HbSβ⁺ (beta-plus): Some hemoglobin A is still produced, in amounts that vary by the specific genetic variant. This generally produces a milder course, with less frequent and less severe complications than HbSS.

Rare compound genotypes: HbSD, HbSE, and HbS-O Arab

Less commonly, a person inherits one HbS gene paired with a gene for another abnormal hemoglobin — D, E, or O. These are genuinely rare, and severity varies a great deal depending on the exact pairing: HbS-O Arab tends to behave much like severe HbSS, while HbSE is more often associated with a milder course, though case reports describe real variability. Because these genotypes are uncommon, they're sometimes under-recognized by labs unfamiliar with them. We go deeper on each of these, plus HbS-HPFH, in our rare genotypes guide.

Why knowing your exact genotype matters

Two people can both carry an "SCD" diagnosis on paper and have very different day-to-day experiences, risk profiles, and monitoring needs. Knowing your specific genotype can help you and your care team:

• Anticipate which complications to screen for (for example, prioritizing dilated eye exams if you have HbSC)
• Interpret lab results like hemoglobin level and hemoglobin electrophoresis percentages in proper context
• Have more precise conversations with new specialists, especially if you relocate or switch care teams
• Understand why your experience might differ from another SCD warrior's — genotype is one of several factors, alongside things like co-inherited alpha thalassemia and individual fetal hemoglobin (HbF) levels

Where complementary wellness support fits in

None of this changes the fundamentals of SCD management, which remains squarely in the hands of your hematology team — genotype-specific monitoring, hydroxyurea or other disease-modifying therapies where appropriate, and prompt care for complications. What we hear from many warriors in this community is a desire for additional, everyday wellness support alongside that medical care: steady hydration habits, gut-friendly nutrition, and consistent self-care routines. That's the space HalfMoon Labs' fermented Sorghum Bicolor and Papaya Leaf formula is designed for — a complementary wellness product, not a substitute for anything your hematologist has prescribed.

Frequently asked questions

Is one genotype of sickle cell disease "worse" than the others?

Generally, HbSS and HbSβ⁰-thalassemia tend to run the most severe clinical course on average, while HbSC and HbSβ⁺-thalassemia tend to be milder — but these are population-level tendencies, not guarantees for any one person. Individual severity varies widely even within the same genotype.

Can my genotype change over time?

No. Genotype is fixed at conception and doesn't change. What can change is how a genotype is managed and monitored as treatments and your own health needs evolve.

How is genotype actually determined?

In the U.S., it's typically identified through newborn screening, and confirmed or re-confirmed later in life via hemoglobin electrophoresis or genetic testing, which separates and measures the different hemoglobin types present in the blood.

Is sickle cell trait the same as having sickle cell disease?

No. Sickle cell trait (HbAS) means carrying one copy of the HbS gene alongside one normal gene. It's a carrier state, not a disease, and most people with the trait live symptom-free, though they can pass the HbS gene to their children.

This article is for educational purposes only and is not medical advice. HalfMoon Labs' fermented Sorghum Bicolor and Papaya Leaf formula is intended as complementary wellness support and is not a treatment, cure, or preventive therapy for sickle cell disease or any of its genotypes or complications. Always consult your hematologist or care team before making any changes to your treatment plan.

Sources: CDC — About Sickle Cell Disease; Cleveland Clinic — Sickle Cell Disease; Merck Manual — Hemoglobin S–Beta-Thalassemia Disease; Healthline — Types of Sickle Cell Disease.