HbSS sickle cell disease, also called sickle cell anemia, is the most common and usually the most severe form of sickle cell disease. It occurs when a person inherits the sickle hemoglobin gene from both parents, so almost all of their hemoglobin is hemoglobin S. Red cells stiffen into a sickle shape, block small blood vessels and break down early. The result is lifelong anemia, pain crises and a risk of organ damage. It is diagnosed through newborn screening or a hemoglobin test, and managed with infection prevention, hydroxyurea, transfusions and, for some patients, a stem cell transplant.
I have looked after people with HbSS from their first clinic visit as infants through to adulthood. Care has changed dramatically, and most children born with HbSS in countries with good healthcare now reach adulthood. Knowing what to watch for makes a real difference.
What Is HbSS Sickle Cell?
Normal adult hemoglobin (HbA) has two alpha and two beta globin chains. In sickle cell disease, a single-letter change in the beta-globin gene replaces glutamic acid with valine at position 6. The result is hemoglobin S (HbS).
“HbSS” means both beta-globin genes carry the sickle mutation (the person is homozygous). This distinguishes it from other forms of sickle cell disease:
| Genotype | What is inherited | Typical severity |
|---|---|---|
| HbAS (sickle cell trait) | One sickle gene, one normal gene | A carrier state, usually without symptoms |
| HbSS (sickle cell anemia) | Two sickle genes | Usually severe |
| HbS/β0 thalassemia | One sickle gene, one gene producing no beta globin | Usually severe, similar to HbSS |
| HbSC | One sickle gene, one hemoglobin C gene | Usually milder, but with specific eye and bone risks |
| HbS/β+ thalassemia | One sickle gene, one gene producing reduced beta globin | Often milder |
HbSS is inherited in an autosomal recessive pattern. When both parents carry the trait, each pregnancy has a one-in-four chance of a child with HbSS, a one-in-two chance of a carrier, and a one-in-four chance of a child with neither gene. The sickle gene is most common in people with ancestry from sub-Saharan Africa, the Mediterranean, the Middle East and India, because carrying one copy offers some protection against severe malaria.
Why Red Cells Sickle
When sickle hemoglobin releases oxygen, its molecules stick together into long, rigid polymers. These fibers deform the cell into the classic sickle shape. Dehydration, cold, infection, low oxygen and acidosis all promote sickling.
Two main problems follow. First, the rigid cells and the damaged, sticky vessel lining cause vaso-occlusion: small vessels clog, starving tissues of oxygen and causing pain and organ injury. Second, sickle cells survive only about 10–20 days instead of the normal 120, a process called hemolysis. The bone marrow works overtime to keep up, but hemoglobin in HbSS typically settles around 6–9 g/dL.
Symptoms and Complications
Symptoms usually begin in the second half of the first year of life, as protective fetal hemoglobin (HbF) falls. Common features include:
- Chronic anemia, causing fatigue, pallor and reduced exercise tolerance
- Vaso-occlusive pain crises in bones, the chest, the back or the abdomen
- Dactylitis, painful swelling of the hands and feet in infants
- Jaundice and gallstones from ongoing hemolysis
- Delayed growth and puberty
Serious complications include:
- Infection: the spleen is damaged early in childhood (functional asplenia), leaving children vulnerable to pneumococcal sepsis
- Acute chest syndrome: chest pain, fever and new lung shadowing on X-ray, a leading cause of hospital admission and death
- Stroke: both overt and “silent” strokes can occur, even in young children
- Splenic sequestration: sudden trapping of blood in the spleen, causing a rapid fall in hemoglobin
- Aplastic crisis: a temporary shutdown of red cell production, typically triggered by parvovirus B19
- Chronic organ damage: to the kidneys, lungs (pulmonary hypertension), eyes (retinopathy), hips (avascular necrosis) and skin (leg ulcers), plus priapism in males
Diagnosis
Many countries include sickle cell disease in newborn screening using a heel-prick blood sample, which allows preventive care to start before symptoms appear. In older children and adults, and to confirm a screening result, diagnosis relies on hemoglobin electrophoresis, high-performance liquid chromatography (HPLC) or isoelectric focusing.
In HbSS, these tests show mostly HbS, a variable amount of HbF and no HbA (unless the person was recently transfused). The blood count shows anemia with a raised reticulocyte count, and the blood film shows sickle cells and target cells. HbS/β0 thalassemia can look very similar, so family studies or DNA testing, along with red cell size, may be needed to tell them apart. Prenatal testing and preimplantation genetic diagnosis are available to couples who are both carriers.
Treatment and Management
Good care is proactive, not just reactive. The foundations are:
- Infection prevention: daily penicillin from early infancy to at least age five, plus a full vaccination schedule including pneumococcal, meningococcal and annual influenza vaccines
- Stroke screening: yearly transcranial Doppler ultrasound in children, typically from age 2 to 16; abnormal results lead to regular transfusions
- Hydroxyurea: raises HbF, which reduces sickling. It lowers the frequency of pain crises and acute chest syndrome and is offered from infancy.
- Transfusion: simple or exchange transfusion for severe anemia, acute chest syndrome, stroke and stroke prevention
- Pain crisis care: prompt, adequate pain relief, fluids and warmth, with a personal care plan
- Curative options: a stem cell transplant from a matched sibling can cure HbSS, and gene therapies are now approved in some countries for selected patients
Other disease-modifying medicines are available in some settings. Folic acid is often given to support the marrow’s high turnover.
When to See a Doctor
People with HbSS need a regular specialist review. Go to the emergency department urgently for:
- A fever of 38.5°C (101.3°F) or higher
- Chest pain or difficulty breathing
- Sudden weakness, facial droop, confusion or trouble speaking
- Severe pain not controlled at home
- A rapidly enlarging spleen or sudden pallor in a child
- A painful erection lasting more than a few hours
Our sickle cell guide covers the other genotypes and day-to-day living in more detail.
Frequently Asked Questions
Is HbSS the same as sickle cell trait?
No. Sickle cell trait (HbAS) means carrying one sickle gene. It usually causes no symptoms. HbSS means two sickle genes and causes sickle cell disease.
Can HbSS sickle cell be cured?
A stem cell transplant, usually from a matched sibling, can cure it, and gene therapies offer another route for selected patients. These treatments carry significant risks, so most people are managed with hydroxyurea and preventive care.
What is the life expectancy with HbSS?
It has improved greatly with newborn screening, penicillin, vaccines, hydroxyurea and stroke screening. It remains shorter than average, and it depends heavily on access to specialist care.
Can I prevent pain crises?
You can reduce them. Staying well hydrated, avoiding extreme cold and overexertion, treating infections early and taking hydroxyurea consistently all help, although some crises happen without an obvious trigger.
