Sickle Cell Trait and Sickle Cell Screening Tests

What is sickle cell trait?

Sickle cell trait means having one gene for a condition called sickle cell anaemia. This in itself does not normally cause problems and sickle cell trait is not considered as a ‘disease’. Rarely, it can cause problems or complications, which mainly occur under conditions of severe physical stress (explained below).

Sickle cell trait is important because your children can inherit the sickle cell gene. If BOTH parents have sickle cell trait, their children could get a double dose of the sickle cell gene, which would give them a serious condition called sickle cell disease. This is relevant if you are pregnant or wanting to start a family.

What are sickle cell anaemia and sickle cell disease?

Sickle cell anaemia (SCA) is a serious condition which is genetic (inherited). It affects the red blood cells in the blood. With SCA, the red blood cells have a tendency to go out of shape and become sickle-shaped (like a crescent moon) - instead of their normal doughnut/disc shape. This can cause various problems such as episodes of pain, infections and various complications. In between the episodes of illness, people with SCA feel well.

Sickle cell disease (or sickle cell disorders) are a group of conditions that cause red cells to become sickle-shaped. By far the most common is sickle cell anaemia. Indeed, the terms 'sickle cell anaemia' and 'sickle cell disease' are often used interchangeably. However, there are various other disorders that are classified as subtypes of 'sickle cell disease' with each having a slightly different genetic makeup. Examples are sickle cell/beta thalassaemia and sickle cell/HbC. The symptoms, diagnosis and treatment of these conditions are similar to sickle cell anaemia.

Who gets sickle cell trait or sickle cell disease?

Anyone can have sickle cell trait, but it is most common in people whose origin is Black African, Black Caribbean or Black British. It also occurs in people who originate from the Middle East, India and Eastern Mediterranean areas. In other populations, sickle cell trait is unusual but can occur.

In England, about 240,000 people carry a sickle cell gene. About 1 in 2,400 babies born have sickle cell disease, but this is an average figure. Some urban areas such as London have much higher rates, for example: 6 in 100 pregnant women carrying a gene for a haemoglobin disorder (mostly sickle cell trait) and 1 in 300 newborn babies having sickle cell disease.

What causes sickle cell trait and sickle cell disease?

You inherit haemoglobin genes from both parents. One sickle cell gene gives you sickle cell trait; two sickle cell genes give you sickle cell disease.

How are sickle cell trait and sickle cell disease diagnosed?

The diagnosis is made from a blood test. The blood sample is analysed to see what type of haemoglobin is present in the blood. (This is done using tests such as electrophoresis or other methods.) This can diagnose most cases of sickle cell trait and sickle cell disease. Sometimes the result is unclear and a further blood test is needed.

Sickle cell tests for pregnant women, babies and couples

In England, the NHS sickle cell and thalassaemia screening programme has been set up. This offers pregnant women and newborn babies screening for sickle cell conditions (and for some other blood disorders such as thalassaemia). In other parts of the UK, you can ask your doctor for a sickle cell test.

Tests for pregnant women

In England, from October 2008, a sickle cell screening programme is to be part of antenatal (pregnancy) care. In areas where sickle cell trait is common, a blood test for sickle cell conditions will be offered to every pregnant woman. In areas where sickle cell trait is not common, all pregnant women will be asked about their family origins (using a specially designed family origin questionnaire). If your family origins suggest that sickle cell trait is possible (or if you are unsure), then you will be offered the sickle cell blood test.

If the result shows that you carry a sickle cell gene, then a test is also offered to the baby's father (if possible). The results of both parents' tests will help to decide whether your baby could be affected by sickle cell disease. The results will be explained to you.

If there is a chance that the baby could inherit sickle cell disease, you will be offered counselling to discuss whether you would like to have a further test for the unborn baby (a prenatal test). A prenatal test finds out whether the unborn baby actually has sickle cell disease. If so, you will be offered counselling to discuss how this could affect the baby, and whether you want to continue with the pregnancy.

Would sickle cell disease make my baby ill during pregnancy?
No; it does not affect the baby while in the womb. Symptoms start from around age three months, and treatment for sickle cell disease should begin by this age.

When is the best time to have a test?
If you are pregnant, the ideal time to have a sickle cell blood test for yourself is before 10 weeks pregnant. This allows more time to test your partner or your baby, if needed. You can ask your doctor for a test early in pregnancy if it is not already offered to you at that time. However, tests can still be done at a later stage.

A prenatal test (on the unborn baby) can be done from 10 weeks' pregnant onwards, depending on the type of test used. The usual tests offered are chorionic villus sampling (CVS) or amniocentesis.

Should I and my partner have tests before starting a family?

Women or couples may want to be tested for sickle cell trait before starting a family, especially if their family origins make sickle cell trait more likely. The UK’s Sickle Cell Society and many health professionals encourage awareness of sickle cell trait and early testing. You can ask your doctor for a sickle cell test.

The advantage of having tests before you become pregnant, is that you will know whether or not there is a possibility that your baby could inherit sickle cell disease. This may be helpful when making decisions about pregnancy. For example, you may want to have a prenatal test during pregnancy if there is a risk of sickle cell disease for the baby.

Tests for newborn babies

In the UK, all newborn babies are offered a 'bloodspot test' at 5-8 days after birth. This tests for a number of medical conditions which are considered important because early treatment makes a difference. The test is done by taking a small spot of blood from the baby's heel.

In England, the bloodspot test now includes testing for sickle cell disease. You will be given the results about six weeks later.

If the baby has sickle cell trait, no action or treatment is needed. If the baby has a sickle cell disease, the result will be explained. You will be given a clinic appointment to check the diagnosis and start treatment. Treatment should begin by the time the baby is three months old.

The rest of this leaflet is about sickle cell trait only.

Are there any complications of sickle cell trait?

Complications of sickle cell trait are not common. Most of the complications which do occur are due to extreme physical conditions, and so are probably preventable. The possible complications are:

Complications of severe low oxygen conditions or severe dehydration

These can occur in conditions where oxygen is extremely low - such as flight in an unpressurised aircraft, very high altitude or problems during a general anaesthetic. Also, if you become severely dehydrated (lack of water in the body).

In these situations, sickle cells can form and can block small blood vessels. This may cause episodes of pain in bones, muscles or the spleen. If in the spleen it is called 'splenic infarction' and may cause pain in the abdomen (tummy) or chest. These problems may be severe enough to make you very unwell and to need treatment in hospital. They will usually clear up with treatment and when oxygen and hydration levels are back to normal.

Complications of severe physical exercise

Sometimes people can become seriously ill as a result of extreme physical training, particularly if it is a forced pace, under very hot conditions, if they are unused to the training, or if they do not drink enough fluid. Anyone can become ill under these conditions, but people with sickle cell trait are probably at higher risk.

In these conditions, people with sickle cell trait may get pain episodes or pain in the spleen (as explained above). There is also a risk of other serious problems, which are:

• Exertional heat illness (heatstroke).
• Rhabdomyolysis (a dangerous complication of heatstroke or over-exertion, affecting the kidneys).
• Exercise-related death (sudden unexplained death during exercise).

Studies from the USA which looked at military training found higher rates of these problems for people with sickle cell trait doing severe physical training. Further research found that these problems can probably be prevented by taking sensible precautions during training.

How can complications of severe exercise be prevented?
Details are given in the National Athletic Trainers' Association guidelines (reference below). As a summary:

• Tell your trainer, sports association, doctor and nurse that you have sickle cell trait, and make sure they are aware of the guidelines.
• Avoid extremes such as heat, very high altitude, exertion to the point of collapse, or sudden increase in exercise without proper training. You can still take part in sports if you take precautions. There are professional athletes who have sickle cell trait.
• When exercising, drink enough fluid. Have breaks for drinks, rest and cooling.
• Sports where you can 'pace yourself' are safer than a forced pace.
• If you have symptoms such as pain or difficulty breathing, stop, report your symptoms, rest and rehydrate. Get medical advice if symptoms don't improve quickly.
• Build up your training gradually. If going to a high altitude, take time to acclimatise.
• If you also have asthma, make sure it is treated and well-controlled.
• Extreme activities (such as flying in unpressurised aircraft or visiting very high altitudes) may not be suitable - you will need medical advice.
• As with any condition affecting the blood, it is healthier not to smoke.

Other complications

There are some other conditions which seem to be slightly more common in people with sickle cell trait. However, there is still uncertainty as to how far these conditions are linked to sickle cell trait. Possibly, you may be more prone (compared to people without the trait) to:

• Haematuria (blood in the urine) - this may be noticeable, or in a tiny quantity found only on urine tests. It may affect about 1 in 50 people with sickle cell trait. If you have blood in the urine, it should be investigated (tests done) to see if there is any particular cause. Treatment is needed in some cases.
• Urinary tract infections (bladder or kidney infections).
• Pulmonary embolus or DVT (a blood clot in the lung or leg).

To help prevent these problems, advice is to avoid dehydration (drink enough fluid). To prevent a pulmonary embolus or DVT, keep mobile and move your legs when on a long journey or flight. See separate leaflets called 'Deep Vein Thrombosis (DVT)', 'Deep Vein Thrombosis - Prevention When Travelling' and 'Pulmonary Embolism' for more details.

Further information and support

Sickle Cell Society

54 Station Road, London, NW10 4UA
Tel: 020 8961 7795 Web: www.sicklecellsociety.org

The Sickle Cell Information Center

A USA website with lots of information
Web: www.scinfo.org

Brent Sickle and Thalassaemia Centre

122 High Street, Harlesden, London NW10 4SP
Web: www.sickle-thalassaemia.org

Royal College of Obstetricians and Gynaecologists

Website has information about prenatal tests (chorionic villus sampling and amniocentesis).
Web: www.rcog.org.uk