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Genetic testing

Family cascade testing

How a single genetic diagnosis flows through a family - testing relatives efficiently once a variant is known.

Key facts

At a glance

  • The principle: once a family’s specific variant is identified, relatives need only a simple targeted test - quick, definitive and usually free of ambiguity.

  • The arithmetic: first-degree relatives of a carrier typically have a 50% chance; testing radiates outwards from each new positive.

  • A negative is golden: relatives who test negative for the family variant generally return to population risk and exit intensive screening.

  • The human side: informing relatives falls to families, not doctors - genetics services provide letters and support for the conversations.

  • Access: cascade testing is free on the NHS for at-risk relatives in most programmes, and available privately within weeks.

The full picture

What this test involves, and how to get it

Cascade testing is genetics’ multiplier: identifying one person’s disease-causing variant converts testing for their entire family from open-ended searching into a single targeted question - do you carry this specific variant, yes or no? The test is quicker and cheaper than the original discovery, and its answers are usually clean. Each first-degree relative of a carrier - parents, siblings, children - typically carries a 50% chance, and the cascade radiates outward from every new positive. Both answers pay: positives enter surveillance and prevention at the right age (transformative in conditions like Lynch syndrome, familial hypercholesterolaemia and BRCA-related risk, and in FH the cascade extends to children), while true negatives generally return to population-level risk and are released from intensive screening they would otherwise have inherited by anxiety.

The delicate machinery is human: UK confidentiality practice means clinicians cannot contact your relatives directly, so genetics services equip you instead - family letters that explain the variant and how relatives can seek testing, plus counselling support for conversations that can stir old family currents. Relatives take the letter to their GP for referral into their own regional genetics service, where cascade testing for an established familial variant is NHS-funded and prioritised; relatives abroad or wanting speed can arrange targeted testing privately within weeks at accredited laboratories. Predictive cascade results fall under the UK insurance code - not requested by insurers at standard cover levels - and each relative receives their own counselling, because the right to decline testing travels with the letter too.

A quiet reminder

This guide is for information, not medical advice.

Your own clinician knows your history and can tell you which parts apply to you. Next review of this page: 2027-09-27.

Frequently asked

Common questions about Family cascade testing.

Quick, plain-English answers to what people ask us most.

  • What does Family cascade testing involve?

    Family cascade testing looks at specific genes or genetic markers, usually from a blood or saliva sample, to identify inherited variants that may be relevant to your health or that of your family. It's typically requested because of a personal or family history that raises the possibility of a specific inherited condition. Results are usually discussed with genetic counselling support given the personal implications involved.

  • Who should consider this kind of testing?

    This is usually most relevant for people with a relevant family history, a personal diagnosis that suggests a genetic cause, or specific ethnic or population risk factors. A genetic counsellor or specialist can help assess whether testing is likely to be useful in your particular situation before you proceed. Testing is a personal decision, and support is available to help you weigh up the potential implications beforehand.

  • Do I need to prepare beforehand?

    Most genetic tests need no physical preparation beyond providing a blood or saliva sample, but pre-test counselling is often recommended so you understand what a result could mean. This is different from most other tests, since the implications can extend to other family members as well as yourself. The clinic will explain what to expect during the consent and counselling process.

  • What happens during testing?

    The sample collection itself is usually quick and straightforward — typically a blood draw or a saliva/cheek swab. Analysis is carried out in a specialist laboratory and takes considerably longer than a standard blood test because of the complexity involved. You'll usually have a consultation both before and after testing to discuss what's involved and what the result means.

  • Are there any risks to having the test?

    The physical risks of sample collection are minimal, similar to a standard blood test. The more significant considerations are emotional and practical — how you might feel about a result, and potential implications for insurance, family planning or relatives. Genetic counselling before testing is designed to help you think through these issues in advance.

  • How long does it take to get results?

    Genetic tests generally take longer than routine blood tests, often several weeks, because of the detailed laboratory analysis involved. Your clinician will give you an expected timeframe specific to the test being carried out. Results are usually delivered in a follow-up consultation rather than a written report alone.

  • What happens if the result is positive?

    A positive result means a specific genetic variant has been identified, and a specialist will explain what this means for your health risk and any recommended next steps, such as increased monitoring or preventative options. It may also have implications for blood relatives, who can be offered testing of their own if relevant. You'll be supported through this discussion rather than simply given a result on paper.

  • Is genetic testing available on the NHS?

    NHS genetic testing is generally available where specific clinical criteria are met, such as a strong family history, though this can involve a wait for assessment and results. Private genetic testing can offer quicker access and may be considered by people who don't meet NHS eligibility criteria but still want to understand their risk. Cost varies by provider and varies depending on the scope of the test.

  • How accurate is this kind of test?

    Modern genetic testing is highly accurate at detecting the specific variants it's designed to look for, when carried out in an accredited laboratory. However, a negative result doesn't rule out all possible genetic contributions to a condition, and results are best interpreted with specialist input. Your genetic counsellor or specialist can explain the specific accuracy and limitations relevant to your test.

  • How do I arrange this kind of testing privately?

    You can typically arrange an initial consultation with a private clinic or genetic specialist to discuss whether testing is appropriate for you. This usually includes pre-test counselling, the test itself, and a follow-up appointment to discuss results. Contact the clinic to ask about availability and what the process involves.