Sickle Cell Disease: A Complete A–Z Glossary

A plain-English guide for patients, parents, carers and families in the UK

This glossary explains common sickle cell terms you may hear from doctors, nurses and other healthcare professionals in the NHS. It covers the condition itself, symptoms, pain crises, blood tests, treatments, complications, genetics and everyday life.

### 1\. Understanding sickle cell disease


Sickle cell disease (SCD) is an inherited blood condition. It affects haemoglobin, the protein in red blood cells that carries oxygen around the body.

In sickle cell disease, some red blood cells can become rigid, sticky and crescent-shaped. They can break down too quickly or block small blood vessels, causing pain and other complications.

* Red blood cells: Cells that carry oxygen from the lungs to the rest of the body.

* Haemoglobin (Hb): The protein inside red blood cells that carries oxygen.

* Sickling: When red blood cells change shape and become more likely to block blood vessels.

* Sickle cell anaemia (SCA): A form of sickle cell disease, usually associated with the HbSS genotype.

* Sickle cell trait: Having one sickle haemoglobin gene. This is different from having sickle cell disease.

* Genetic condition: A condition caused by a change in genetic information inherited from parents.

* Inherited: Passed from biological parents to their children through genes.

* Chronic condition: A health condition that continues over a long period and needs ongoing care.

### 2\. A–Z glossary

### A

Acute chest syndrome (ACS)

A serious complication affecting the lungs. Symptoms may include chest pain, fever, coughing and difficulty breathing. It requires urgent hospital assessment.

Anaemia

A low level of haemoglobin or healthy red blood cells. It can cause tiredness, weakness, dizziness and breathlessness.

Analgesia

Medical treatment used to relieve pain.

Antibiotics

Medicines used to treat bacterial infections. Some children with sickle cell disease are prescribed daily penicillin to help prevent serious infections.

Aplastic crisis

A sudden reduction in red blood cell production, sometimes caused by parvovirus B19. It can lead to a rapid fall in haemoglobin.

### B

Bilirubin

A yellow substance produced when red blood cells break down. High levels can contribute to jaundice.

Bone marrow

The soft tissue inside certain bones that produces red blood cells, white blood cells and platelets.

Blood transfusion

A procedure in which donated blood or red blood cells are given through a vein.

Blood group and antibody screen

Tests performed before a transfusion to help find compatible blood and reduce the risk of reactions.

### C

Carrier

Someone who has one copy of a particular haemoglobin gene variant but does not usually have the associated disease.

Chelation therapy

Treatment with medicines that remove excess iron from the body, often needed after repeated transfusions.

Cholelithiasis (gallstones)

Hardened deposits in the gallbladder. They can develop because red blood cells break down more quickly in sickle cell disease.

Chronic pain

Pain that persists or recurs over a long period, sometimes even outside an acute pain crisis.

Clinical nurse specialist (CNS)

A specialist nurse who provides advice, care coordination and support for people with sickle cell disease.

Crisis (pain crisis)

An episode of pain caused by blocked blood flow. It may affect the bones, joints, chest, abdomen or other parts of the body.

### D

Dehydration

When the body loses more fluid than it takes in. It can contribute to a pain crisis.

Diagnosis

Identifying a condition using symptoms, medical history and appropriate tests.

Dactylitis

Painful swelling of the hands and feet, especially in babies and young children with sickle cell disease.

DNA

The material in cells that carries genetic instructions.

Disease-modifying treatment

Treatment intended to reduce the underlying disease process or the frequency of complications, rather than only relieve symptoms.

### E

Electrophoresis / haemoglobin analysis

Laboratory testing used to identify different types of haemoglobin. It helps establish a person's haemoglobin genotype.

Emergency care plan

Written information explaining how a person's sickle cell disease should be managed during an emergency.

Exchange transfusion

A procedure in which some of a person's blood is removed and replaced with donor red blood cells. It may be used for serious complications, including certain strokes or acute chest syndrome.

Enlarged spleen

A spleen that is larger than usual. In some children, blood can become trapped there, causing a dangerous fall in haemoglobin.

### F

FBC (full blood count)

A blood test measuring haemoglobin and the numbers of red cells, white cells and platelets.

Folic acid

A vitamin needed to make red blood cells. It may be prescribed to some people with sickle cell disease.

Fetal haemoglobin (HbF)

A form of haemoglobin usually found in unborn babies and newborns. Higher levels can reduce red blood cell sickling.

Fatigue

Persistent tiredness or lack of energy, which may be associated with anaemia, pain or disrupted sleep.

### G

Gallstones

Small, hard deposits in the gallbladder that can cause abdominal pain or inflammation.

Gene

A section of DNA containing instructions for a particular biological function.

Genetic counselling

A discussion with a trained professional about inherited conditions, test results and the chance of passing a condition to children.

Genotype

The combination of haemoglobin gene variants a person has, such as HbSS, HbSC or HbAS.

### H

Haemoglobin (Hb)

The oxygen-carrying protein inside red blood cells.

HbAS

The usual abbreviation for sickle cell trait: one haemoglobin A gene and one haemoglobin S gene.

HbSS

A genotype in which both haemoglobin genes are sickle genes. It causes sickle cell anaemia.

HbSC

A genotype involving haemoglobin S and haemoglobin C. It causes a form of sickle cell disease.

HbS beta-thalassaemia

A form of sickle cell disease involving haemoglobin S and a beta-thalassaemia gene variant.

Hydroxycarbamide (hydroxyurea)

A medicine that increases fetal haemoglobin and can reduce pain crises and some other complications.

Hydration

Taking in enough fluid to maintain the body's fluid balance.

### I

Infection

An illness caused by germs. Certain infections can become serious quickly in people with sickle cell disease.

Immunisation

Vaccination that helps protect against infections.

Ischaemia

Reduced blood supply to a part of the body, which can damage tissue.

Iron overload

A build-up of excess iron in the body, sometimes caused by repeated blood transfusions. It can damage organs if untreated.

### J

Jaundice

Yellowing of the skin or whites of the eyes due to increased bilirubin.

Joint pain

Pain in joints such as the hips, knees, shoulders or elbows. It may occur during a pain crisis or from longer-term complications.

### K

Kidney complications

Problems with kidney function that may develop over time in sickle cell disease.

Karyotype

A picture of a person's chromosomes. It is not a routine test for diagnosing sickle cell disease; haemoglobin testing is normally used.

### L

Leg ulcer

An open sore, often around the lower leg or ankle, that can be slow to heal.

Leucocytes (white blood cells)

Cells that help the body fight infections.

Lung complications

Problems affecting breathing or lung function, including acute chest syndrome and pulmonary hypertension.

### M

Microalbuminuria / albuminuria

Small or larger amounts of the protein albumin in urine. This can be an early sign of kidney damage.

Mutation / genetic variant

A change in DNA. Certain haemoglobin variants can cause sickle cell disease.

Multidisciplinary team (MDT)

Healthcare professionals from different specialties who work together to provide care.

Myocardial infarction

The medical term for a heart attack. Chest pain in someone with sickle cell disease always needs careful assessment.

### N

Newborn blood spot test (heel-prick test)

A screening test offered to babies in the UK, usually when they are around five days old. It screens for sickle cell disease and other conditions.

Nephropathy

Kidney disease or kidney damage.

Neurological symptoms

Symptoms involving the brain or nervous system, such as weakness, confusion, severe headache or speech difficulties. Sudden symptoms may indicate a stroke.

### O

Oxygen saturation (SpO₂)

An estimate of the percentage of haemoglobin carrying oxygen, measured with a finger probe.

Opioids

Strong pain-relieving medicines, such as morphine, sometimes used for severe pain crises.

Osteonecrosis (avascular necrosis)

Damage to bone caused by reduced blood supply. It commonly affects the hip or shoulder and can cause persistent pain and reduced movement.

### P

Pain management

A plan for treating pain, which may include medicines, fluids where appropriate, warmth, rest and other supportive measures.

Penicillin prophylaxis

Regular preventive penicillin prescribed to some children to reduce the risk of serious bacterial infections.

Platelets

Blood components that help blood clot.

Priapism

A prolonged erection that may be painful and can occur in sickle cell disease. An erection lasting four hours or longer is a medical emergency.

Pulmonary hypertension

Abnormally high blood pressure in the blood vessels supplying the lungs.

Parvovirus B19

A virus that can temporarily stop red blood cell production and trigger an aplastic crisis.

### Q

Quality of life

How a condition affects a person's daily activities, relationships, sleep, education, work and emotional wellbeing.

Quality of life assessment

A conversation or questionnaire used by a healthcare team to understand how symptoms affect everyday life.

### R

Reticulocytes

Young red blood cells released by the bone marrow. Their number helps clinicians assess red blood cell production.

Red cell exchange

Another name for exchange transfusion.

Retinopathy

Damage to the retina at the back of the eye. Sickle cell disease can affect the retinal blood vessels, so eye checks are important.

Recurrent pain

Pain that occurs repeatedly, whether as separate crises or as persistent pain between crises.

### S

Sickle cell trait

Having one haemoglobin S gene, usually without sickle cell disease. A carrier can pass the gene to their children.

Splenic sequestration

A dangerous complication in which blood becomes trapped in the spleen, causing the spleen to enlarge and haemoglobin to fall suddenly.

Spleen

An organ that helps filter the blood and fight infection. In sickle cell disease, it can become damaged over time.

Stroke

Brain injury caused by interrupted blood flow or bleeding. Sickle cell disease increases the risk of stroke.

Stem cell transplant

A treatment that can potentially cure sickle cell disease for some people. It uses blood-forming stem cells from a suitable donor and carries significant risks.

Supportive care

Treatment that relieves symptoms, prevents complications and supports overall wellbeing.

### T

Thalassaemia

A separate group of inherited blood conditions affecting haemoglobin. Some thalassaemia gene variants can combine with HbS to cause sickle cell disease.

Transcranial Doppler (TCD)

An ultrasound scan of blood flow in the brain, used in children with certain forms of sickle cell disease to assess stroke risk.

Transfusion reaction

An unwanted response to a blood transfusion. Symptoms can include fever, chills, pain or breathing problems; some reactions occur days or weeks later.

Thrombosis

Formation of a blood clot inside a blood vessel.

### U

Urinalysis

A test of urine used to check for signs of kidney problems, infection or other abnormalities.

Ultrasound

A scan using sound waves to produce images of organs or blood flow. It may be used in assessments for sickle cell complications.

### V

Vaso-occlusion

Blockage of small blood vessels by sickled cells, reducing blood flow to tissues.

Vaso-occlusive crisis (VOC)

A painful episode caused by vaso-occlusion. It is one of the most common reasons for emergency care in sickle cell disease.

Vaccination

Immunisation against infectious diseases. Keeping vaccinations up to date is particularly important for people with sickle cell disease.

Venepuncture

Taking blood from a vein, usually with a needle in the arm or hand.

### W

White blood cells (WBCs)

Cells involved in fighting infection. Their levels may be higher than usual in sickle cell disease, even without an infection.

Wellbeing

A person's physical, emotional and social health, including how well they cope with a long-term condition.

### X

X-ray

An imaging test that uses a small amount of radiation to create pictures of structures inside the body. It may be used when investigating chest symptoms or bone problems.

### Y

Yellowing of the eyes

A visible sign of jaundice. It can occur because red blood cells break down more quickly than usual.

### Z

Zinc

An essential mineral needed for normal growth and immune function. Zinc supplements are not automatically required for everyone with sickle cell disease; ask the clinical team before taking them.

### 3\. Common sickle cell genotypes explained

A genotype is the combination of haemoglobin genes a person inherits. The letters on a blood test can tell you which form of haemoglobin is present.

| Genotype | What it generally means |

| ------------------ | ------------------------------------------------------------ |

| HbAA | Usual haemoglobin type; no sickle gene |

| HbAS | Sickle cell trait; usually not sickle cell disease |

| HbSS | Sickle cell anaemia |

| HbSC | Sickle cell disease involving haemoglobin S and C |

| HbSβ⁰-thalassaemia | Sickle cell disease involving HbS and beta-zero thalassaemia |

| HbSβ⁺-thalassaemia | Sickle cell disease involving HbS and beta-plus thalassaemia |

The severity of sickle cell disease varies between individuals and genotypes. Regular specialist follow-up is important even when someone feels well.

### 4\. Genetics and inheritance: what families should know

Sickle cell disease is inherited. A child usually needs to inherit two relevant haemoglobin gene variants, one from each biological parent, to have the disease.

If both biological parents have sickle cell trait (HbAS), each pregnancy has the following chances:

### 25%

HbAA

Usual haemoglobin

### 50%

HbAS

Sickle cell trait

### 25%

HbSS

Sickle cell anaemia

These probabilities apply independently to each pregnancy; they are not predictions that a family will have one child of each type.

If one parent has a different haemoglobin variant, such as HbC or a thalassaemia variant, the possible outcomes can differ. A GP, haemoglobinopathy team or genetic counsellor can explain individual results.

### 5\. Common abbreviations used in NHS care

| Abbreviation | Full meaning |

| ------------ | ------------------------------------------------------------------------------- |

| ACS | Acute chest syndrome |

| CNS | Clinical nurse specialist |

| DNA | Deoxyribonucleic acid |

| FBC | Full blood count |

| Hb | Haemoglobin |

| HbF | Fetal haemoglobin |

| HbSS | Sickle cell anaemia genotype |

| HbSC | Haemoglobin SC genotype |

| MDT | Multidisciplinary team |

| NHS | National Health Service |

| RBC | Red blood cell |

| SCA | Sickle cell anaemia |

| SCD | Sickle cell disease |

| SCT | Sickle cell trait; in screening, SCT can also mean sickle cell and thalassaemia |

| SpO₂ | Oxygen saturation |

| TCD | Transcranial Doppler |

| VOC | Vaso-occlusive crisis |

| WBC | White blood cell |

### 6\. Warning signs: when to seek urgent help

A glossary can help you understand the condition, but it is also important to recognise symptoms that need urgent treatment.

Call 999 for an emergency

* Sudden facial drooping, weakness, confusion or difficulty speaking.

* Severe difficulty breathing.

* Collapse, unresponsiveness or another life-threatening symptom.

Seek urgent medical assessment

* A temperature of 38°C or higher, or the fever threshold specified in your care plan.

* Chest pain, coughing with breathing difficulty or new breathing problems.

* Severe or unusual pain, especially if your usual treatment is not working.

* Sudden pallor, marked weakness, unusual sleepiness or a swollen abdomen.

* An erection lasting four hours or longer.

Follow the person's individual sickle cell care plan and contact their specialist team when advised. Do not delay emergency care while trying home treatments.

### 7\. Reliable UK information and support

* NHS sickle cell disease information — [Read the NHS guide](https://www.nhs.uk/conditions/sickle-cell-disease/).

* Sickle Cell Society — [Patient and family support](https://www.sicklecellsociety.org/).

* GOV.UK sickle cell and thalassaemia screening — [Screening guidance and resources](https://www.gov.uk/government/collections/nhs-sickle-cell-and-thalassaemia-sct-screening-programme).

These resources can help families understand test results, treatment options, newborn screening and the support available through NHS services.

This glossary is for education and support. It does not replace advice from your sickle cell specialist, GP or NHS care team.