Genetic testing

What is a genetic test?

A genetic test is a medical test, most often carried out on a blood sample, that looks for changes in a person’s genetic make-up. The test may look for changes to chromosomes, which are packages of genetic material, or changes to genes, which are the individual genetic instructions. 

Why are genetic tests carried out?

In a medical setting, genetic tests can be carried out for a number of reasons, including:

  • To help diagnose a suspected genetic condition.
  • To identify the specific underlying genetic change causing a genetic condition.
  • To help determine the chance of developing a genetic condition in the future.
  • To determine whether someone is a carrier of a genetic condition.
  • To clarify the chance of passing a genetic condition on to children.
  • To find out whether a developing baby or embryo has a particular genetic condition.

How are genetic tests carried out?

A medical genetic test is most often carried out by taking a blood sample from the patient’s arm. The genetic material is extracted from blood cells in the laboratory and used in the testing process.  Genetic tests can also sometimes be carried out on saliva samples and skin biopsies. 

Certain genetic tests can be carried out on a pregnancy by taking a sample of amniotic fluid from around the developing baby (in a procedure called amniocentesis), or a piece of material from the placenta (by a procedure called chorionic villus sampling).

There are thousands of genetic tests that are now possible and more are being developed.

How long does it take to get a result from a genetic test?

The length of time it takes to get a result from a genetic test varies considerably. It depends on the specific test being done, the circumstances of the test, for example - is it an urgent test in pregnancy, and the test provider.

Results generally take anything from a few weeks to several months to complete, for example a carrier test for cystic fibrosis might take about 6 weeks through NHS services.  Some tests take many months because some genes are more difficult to analyse than others and the data produced from a test requires a lot of time and care to thoroughly check through.  This is all done to ensure the result given is as accurate as possible. 

The results of a test in pregnancy can be available more quickly because time is an important consideration in making decisions about an ongoing pregnancy and the types of tests possible are generally limited to chromosome tests or testing for known familial genetic changes (mutation/s).

The test provider should be able to tell you how long it will take to get a result.  However, if a test is being carried out through a research study then it is not possible to say how long the result might take or even if an individual result will become available.  

What Types of Genetic Tests are there?

There are many different types of genetic tests carried out in different situations for different purposes. We have explained the main types of medical genetic tests below.

Diagnostic genetic tests

These are carried out to identify or exclude specific genetic conditions in an individual who has symptoms or signs of a genetic condition.  This type of test is most often used to confirm a diagnosis when a condition is suspected.  Diagnostic genetic tests are not yet available for all genetic conditions.  The results of diagnostic tests can help with healthcare management and can provide individuals and families with an explanation for the symptoms experienced.  The vast majority of diagnostic genetic tests in the UK are carried out by clinical geneticists (genetic doctors) in specialist NHS genetic centres.  These professionals are in the best position to know which test/s to do and how to interpret the results, which are sometimes complex.

Carrier tests

These are carried out to see whether a healthy unaffected individual is a carrier of a genetic condition.  Carriers of a genetic condition do not generally have any associated health problems themselves but there may be implications for children.  This type of test is usually offered to individuals with a family history of certain genetic conditions and to people in certain ethnic groups where there is an increased risk of specific genetic conditions. 

Carrier testing can be helpful to couples when they are thinking about starting a family. Carrier testing is usually only offered to adults (18 years+) as the implications are for family planning. It is not yet possible to do carrier testing for all genetic conditions.  

Predictive/presymptomatic genetic tests

This type of test is for someone who has a family history of a serious later onset genetic condition, for example Huntington’s disease, where the symptoms usually start sometime in adulthood. There are no features or signs of the condition at the time of testing. The test can tell someone whether they are likely to go on to develop the condition at some point in the future. 

This type of test is generally only offered to adults (18 years+) as the health implications are only in adulthood and there is a need to respect individual autonomy.  Deciding whether or not to have a predictive/presymptomatic test requires very careful consideration and it is important to discuss all the potential implications with a genetic doctor and/or counsellor.  

Genetic centres across the UK have slightly different processes around predictive/presymptomatic genetic testing.  It is very unlikely they would offer to do the actual test at your first appointment, however in some circumstances this may be done.  Many centres have an initial information gathering appointment, followed by an in-depth discussion appointment, then the test appointment and finally the result appointment. The whole process generally takes a minimum of 6 months. Some people have appointments spread over years while they consider the implications of having the test and wait for the most suitable time in their lives to go ahead with testing. If you are considering this type of test you may want to get referred to your local genetic centre sooner rather than later to get information and find out how your local centre operates. There is no obligation to have the test at any stage.

Whole Exome Tests

This is a new type of genetic testing which is beginning to be carried out (2015) when doctors don’t know where in a person’s genetic make-up to look for the cause of the condition.  Instead of doing a targeted test for a particular genetic change or gene, whole exome testing looks at all genes in one test to search for the genetic change causing the disorder. 

We all have approximately 20,000 genes which comprise only about 2% of our entire genetic make-up (genome).  It is not clear what all the rest of our non-coding DNA is for which is why this type of testing focusses on the gene coding segments where any genetic changes found are thought to be more likely to cause disease.  However, interpreting this information is still complicated as every individual has unique gene sequences and there are lots of tiny genetic differences between all of us, some common and some rare. This makes finding the genetic differences which cause a particular disorder challenging, but advances in our understanding are being made all the time. 

Whole Genome Tests

This is a new type of genetic testing which is not yet being used in clinical practice (2015) but is being used in projects such as the 100,000 Genomes Project, see:  It could, in the future, be used when doctors don’t know where in a person’s genetic make-up to look for the cause of their condition.  The test examines the entirety of a persons genetic make-up, all 20,000 genes and all the non-coding sections of DNA in-between genes.  The function of the non-coding DNA, which comprises about 98% of our genome, is still largely unknown, though some of it is involved in determining when genes are switched 'on' or 'off'. Although there are genetic changes in this non-coding DNA that are important in disease, currently they are much harder to interpret than changes in the gene coding regions. This means that patients and doctors can be left with uncertainty about whether or not a genetic change found is the cause of their symptoms. Over time and with more research, the ability to interpret the results from whole genome testing will improve.

Prenatal diagnostic genetic tests (amniocentesis and CVS tests)

These are diagnostic tests carried out on a pregnancy to look for a genetic condition affecting the developing baby. They are offered when there is an increased risk that the baby could have a serious genetic disorder. 

There can be an increased chance of a genetic condition when there is a family history of a genetic disorder, an abnormal scan result or raised screening test result during pregnancy. It is not possible to test for all inherited conditions or birth defects during pregnancy. The majority of prenatal tests for specific genetic disorders require the genetic cause of the condition in the family to have already been identified.  When there is a family history of a genetic condition it is preferable to look into this and discuss with a genetic professional prior to getting pregnant.  This can clarify the situation and help couples to be fully informed.

Prenatal diagnostic genetic tests are invasive and can be carried out either by a procedure called amniocentesis or by chorionic villus sampling (CVS).  The CVS test can be offered from about 11 weeks of pregnancy and involves taking a small piece from the placenta with a needle through the mother's abdomen.  Amniocentesis can be carried out from about 15 weeks of pregnancy and also involves a needle through the mother's abdomen to take a sample of the amniotic fluid from around the baby.  There is a risk of miscarriage associated with both of these procedures of about 1% or 1 in 100 in addition to the background risk of miscarriage for each stage of pregnancy.  The time it takes to get a result back depends on the genetic test being carried out on the sample.  It could be 3 working days or 2-3 weeks.

Prenatal tests can help parents prepare and make decisions about a pregnancy. Deciding about having a prenatal test is often a difficult decision requiring careful consideration. Parents often find genetic counselling very valuable in this situation.

Non-invasive prenatal screening tests (NIPT)

This is a relatively new type of test which uses fragments of fetal DNA that are present in the mother’s blood stream during pregnancy.  The test is therefore non-invasive with only a blood sample from the mother being required (usually 4 or 5 bottles).  This process can currently (2015) be used to screen a pregnancy for certain chromosome disorders including the three most common chromosome trisomy syndromes Downs, Edwards and Patau syndromes.  It is also beginning to be offered for certain chromosome micro deletion syndromes (conditions that occur when very small pieces of chromosome material are missing). 

This type of test is not yet (2015) available through the NHS but is being offered by private providers under brand names such as Harmony and NIFTY.  The test can be carried out from about 10 weeks of pregnancy and there is no associated increased risk of miscarriage.  Results can take about 2 weeks to come back and about 3% of samples fail to give a conclusive result due to insufficient fetal DNA in the sample. A high-risk or positive result would require confirmation by an invasive test such as amniocentesis. A low-risk or negative test result would be very reassuring.

NIPT is currently a screening test and is not diagnostic.  Studies into the reliability and accuracy are ongoing but have so far indicated a detection rate for Downs syndrome of about 99%.  The accuracy for other conditions, in-particular chromosome micro deletion syndromes is less clear.

For more information about NIPT visit Antenatal Results and Choices:

Non-invasive prenatal diagnostic (NIPD) tests

This type of test is non-invasive and uses fragments of fetal DNA that are present in the mother’s blood stream during pregnancy.  It is now possible to use this technique to test for some single gene disorders under certain circumstances.  It is NOT possible when the altered gene is carried by the mother.  It is possible when the condition could be inherited from the father or could arise as a spontaneous new genetic change (de novo mutation).  NIPD is currently being offered through the NHS for achondroplasia, thanatophoric dysplasia and Apert syndrome when there has been a family history of the condition (2015). 

NIPD is a diagnostic test so an invasive test would not be required to confirm the result.

This area of testing is advancing rapidly and it is becoming possible to offer NIPD for an increasing number of conditions. The North East Thames Regional Genetics laboratory at Great Ormond Street Hospital has some experience of developing bespoke tests. Individual circumstances should be discussed with a genetic professional while planning a pregnancy.  
For more information about NIPD visit the NHS RAPID Project website:

Prenatal fetal sexing test

This test is non-invasive and uses fragments of fetal DNA that are present in the mother’s blood stream during pregnancy.  The test looks for the presence of Y (male) chromosome material.  If Y chromosome material is found then it is very likely the pregnancy is male.  If Y chromosome material is not found then it is very likely the pregnancy is female. This test can be offered when the pregnancy is at risk of a genetic condition that affects one particular sex, such as the X-linked genetic disorder Duchenne Muscular Dystrophy, which affects boys.

The test is available through the NHS when there is a known family history of a sex-linked genetic condition.  The test can be carried out from about 9 weeks of pregnancy and involves a blood sample from the mother. There is no associated increase in miscarriage risk.  The result is usually available in 5 working days. 

Prenatal fetal sexing cannot tell you whether the pregnancy has inherited the condition but can help couples decide whether or not to have an invasive prenatal diagnostic test such as a CVS test.

Preimplantation Genetic Diagnosis (PGD)

PGD is a special type of in-vetro fertilisation (IVF) where the embryos created through the IVF process are tested for a specific genetic condition. Only those embryos without the condition are then used in the IVF treatment to establish a pregnancy.  The option of PGD can be offered to couples who are at risk of having a child with a specific serious genetic condition.  The couple do not need to be experiencing fertility difficulties. PGD is used to prevent a pregnancy being affected by the genetic condition.  Not all genetic conditions are licensed for PGD by the Human Fertilisation and Embryology Authority (HFEA).  For a list of licensed conditions go to

PGD is a lengthy and complex process which often involves travelling to specialist centres.  There are some health risks for a woman having PGD which are associated with the hormone treatment involved.  The chance of having a successful pregnancy leading to the birth of a baby is about 1 in 3 to 4.

PGD is available through the NHS when a couple do not already have a child who is unaffected by the genetic condition.  It is also available privately at a cost of about £8,000 per cycle plus drug costs (£1,000 - £1,200). In England a referral for PGD needs to come from a genetic professional.

The main centre for PGD is Guy's and St Thomas' Centre for Pre-Implantation Genetic Diagnosis, in London  There are other providers of PGD including CARE Fertility

Newborn blood spot screening tests

These are tests carried out on a newborn baby to screen for certain conditions a number of which are genetic.   These tests are offered to all newborn babies in the UK and involve a small blood sample taken from the baby’s heel when they are about 5 days old.  The aim is to identify those babies with a serious treatable health problem so that treatment can be started as early as possible, and may reduce the severity of the condition.  The results generally take a couple of months to come back.

The conditions tested for include: Sickle cell disease (an inherited  blood disorder), phenylketonuria (an inherited metabolic disorder which if untreated can cause intellectual disability), Cystic Fibrosis (a serious genetic condition for which early medical management can improve prognosis), Congenital hypothyroidism (a treatable condition which can be genetic) and Medium-chain acyl Co-A dehydrogenase deficiency (MCADD) (a rare but potentially life threatening genetic disorder which can be managed when it is known about) (Jan 2015).

How can I get a Genetic Test?

NHS Referrals and Testing

The majority of genetic testing in the UK takes place in regional NHS genetic centres where there are accredited laboratories and genetic professionals, who can talk through the tests available and possible implications of the results. 

If you or your child have features of a genetic condition or you have a family history of a genetic condition then you could ask your GP or hospital specialist to refer you to your local genetic service.  Genetic testing is not possible for all genetic conditions but this does not mean that an appointment with a genetic doctor or counsellor would not be useful.  They may be able to explain how the condition has arisen in your family and the implications for other family members including future children.  Support with the emotional and social aspects of a genetic or possible genetic diagnosis is also provided. 

If you are having difficulty getting referred you could suggest your GP contact your local genetic service to enquire whether a referral would be appropriate.  Providing full and accurate information about your family history can help your doctor and the genetic centre assess what might be needed.  It can also sometimes be helpful to request genetic counselling or to see a genetic specialist rather than simply requesting a genetic test.  Once you have been referred to a genetic centre they will be able to tell you what testing is available.

If you are pregnant and have, or have a family history of, a genetic condition then you can be referred to a genetic centre by your GP or midwife on an urgent basis.  It is preferable to do this as early in pregnancy as possible.  It is not possible to test for all genetic conditions in pregnancy and there would be no obligation to have a test even if one were available.  Many people attend for information and support.

If you have questions about a genetic condition and are planning to have children at some stage it may reduce your anxiety in a pregnancy if you are able to have a genetic appointment before getting pregnant. 

Private Testing

We know from the many enquiries we recieve that people are increasingly looking for genetic testing privately. It can be confusing and complicated to search for a private genetic test. We have provided some general information and advice below.

If you have attended an NHS genetic clinic and they are unable to offer you the test, they may be able to direct you to a private provider. Also, some NHS genetic laboratories can carry out tests on a private basis. The test would still need to be arranged through a genetic professional and you would usually be sent an invoice by the lab following the test.

There are an increasing number of private companies and laboratories offering genetic testing.  When searching for genetic tests yourself it is important to check that any test would be carried out to a high standard and the results fully interpreted and explained to you.

Laboratories offering genetic testing in the UK are subject to quality assurance and accreditation.  There are national and European external quality assurance schemes (NEQAS and EMQN), and best practice guidelines produced by the Clinical Molecular Genetics Society (CMGS) and Association of Clinical Cytogeneticists (ACC).  Genetic laboratories in the UK should be accredited with Clinical Pathology Accreditation (CPA) (UK) Ltd, which is the national accreditation body for Medical Laboratories in the UK.

The company offering the test should be registered with the Care Quality Commission (CQC) when in England, Care Commission in Scotland, Health Improvement in Wales and the Regulation & Quality Improvement Authority in Northern Ireland. These are the independent regulators of health care for diagnostic and/or screening services. 

It is always best to enquire about these credentials when considering a test through any particular company or laboratory.  You may want to ask: Is the laboratory that will do the test accredited?  Do they follow best practice guidelines? Is the company registered with the Care Quality Commission?

It is also important to establish in advance how you will get your result.  Will it be by letter, telephone or in person?  Will you get a copy of the lab report?  Will the result be fully explained in an understandable way by a qualified professional (clinical geneticist or genetic counsellor)?  What would happen if the result were to be abnormal or inconclusive?  How would they support you in that situation?  Do they have good links with NHS genetic services?

We are aware of some private providers in the UK, shown below. Genetic Disorders UK does not recommend or endorse these providers.

  • Gene Adviser - An online platform for ordering clinical genetic tests through both NHS and private laboratories. Tests can only be ordered by a medical professional
  • The Gene Clinic - This is a private genetic clinic on Harley Street in London, which is run by Dr Saggar, Consultant Clinical Geneticist
  • The Doctors Laboratory – An independent provider of clinical laboratory diagnostic services including some genetic tests. All tests need to be ordered by a medical professional 

Direct-to-consumer genetic tests

Direct-to-Consumer genetic testing is choosing to purchase a genetic test yourself direct from a genetic test provider without involvement of a healthcare professional. In general, a test kit to collect a DNA sample is sent by post directly to you at home. The kit is often for a mouth swab to collect DNA from cheek cells. In some cases you may need to arrange with your GP practice or local hospital for a blood sample to be taken.  The sample is then sent by you to the laboratory. Your result will come back to you by post, telephone or online.  Some companies have genetic counsellors or other health care professionals available to answer questions. 

The types of tests offered are mostly tests that report on ancestral origins and genetic risks for common health conditions such as diabetes and heart disease. There are limitations with direct-to-consumer genetic tests and concerns have been raised about the accuracy and usefulness of such tests.   Without guidance and support from a healthcare professional it can be difficult to interpret test results and make health decisions on the basis of these.

How much does a genetic test cost?

The cost of a genetic test depends on the complexity of the test and can range from under £100 to £1000s. The cost increases if more than one test is necessary or if multiple family members need to be tested. There will also usually be a consultation fee of around £200- £350.

What are some of the Benefits and Risks of Genetic Tests?

Deciding whether or not to have a genetic test can be difficult. It is your own personal decision.

Before you decide, you need to ensure you have all of the relevant information and have had the opportunity to discuss your questions and concerns with a genetic professional. Genetic test results can bring important benefits, but there are also some risks, limitations and uncertainties associated with genetic tests.  

We have outlined some of the benefits and risks below.


  • A genetic test might be able to tell you for certain about you or your child’s diagnosis.
  • Genetic test results can provide useful information when planning for future children. Finding out you have an increased risk of having a child with a certain genetic condition can give you the opportunity to consider reproductive options or prepare mentally and practically  for your children.
  • As genetic conditions often run in families, your test results may be useful to other family members.

Potential risks and limitations

The process of having genetic testing can cause a range of emotions, such as, anxiety, fear, guilt and relief. It is important to carefully think through the potential implications of the result for you and your family.

  • A definite genetic test result does not mean a treatment is available for the condition.
  • Genetic testing does not always identify the genetic cause of the condition. This does not mean the condition is not genetic. This situation can be very frustrating and leave you with uncertainty.
  • Even when a genetic cause for the condition is found, it is not always possible to predict how mildly or severely someone will be affected by the condition or when symptoms may start.
  • The results of your genetic test may have implications for other members of your family. This can be difficult information to need to pass on to your relatives.
  • Some genetic test results may have implications for insurance.

How do genetic tests for research differ from clinical genetic tests?

Clinical genetic tests are carried out to find out about a genetic condition affecting an individual or family.  The tests are fully validated and carried out in accredited clinical laboratories with specified reporting times.  A healthcare professional will be able to tell you about the test and will interpret and explain the result. 

Research genetic testing is carried out to identify new genes, learn more about how genes work, develop tests for future clinical use and advance  understanding of genetic disorders.  The testing is carried out in research laboratories which are not regulated in the same way as clinical laboratories.  The results are not always available to the patient or their healthcare provider.  In instances where results may become available through a research study it is not possible to say how long a result might take to come back, a year would not be unusual.  Your healthcare provider would have no control over the reporting time and would usually want to confirm any result in a clinical laboratory.

Can Genetic Disorders UK carry out genetic tests?

Genetic Disorders UK does not carry out or arrange any genetic testing. We can help you find out what genetic testing is available, how to access genetic tests and talk through with you the possible pros and cons of testing. If you have any questions about genetic testing please call our Helpline 0800 987 8987 or complete our contact form

Useful LINKS

UK Genetic Testing Network (UKGTN) - A database of NHS validated genetic tests with advice for patients and professionals about genetic testing   

Medline Plus - US National Institute for Health website with trusted health information for patients and families  

Antenatal Results and Choices (ARC) – UK charity offering information and support about tests and options during pregnancy

Guy’s and St Thomas’ Centre for Preimplantation Genetic Diagnosis – NHS centre for preimplantation genetic diagnosis