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Health condition

C1 inhibitor testing

C1 inhibitor testing - level and function, alongside C4 - is the laboratory route to diagnosing hereditary and acquired angioedema, but samples and interpretation have pitfalls worth understanding.

Why trust this guide

  • 01

    Editorial team

    Written by our editorial team from the UK sources listed on each page.

  • 02

    Sourced from guidance

    Checked against current NHS and UK specialist society guidance at the time of review.

  • 03

    Current for 2026

    Reviewed on 2026-09-27 with the next review scheduled for 2027-09-27.

Key facts

The essentials at a glance.

Which gene and test confirm it, who should be tested in the family, and which specialist to see.

  • The screening set: C4, C1 inhibitor antigenic level and C1 inhibitor function

  • Type 1 HAE: low level and function; type 2: normal or high level but low function - function testing is essential

  • Normal C4 during an attack makes C1 inhibitor deficiency unlikely; acquired deficiency (low C1q, later onset) points to an underlying condition

  • HAE with normal C1 inhibitor exists - genetic testing (F12 and other genes) is needed for that group

Understanding the condition

What it is and what happens next.

What causes it, how it is confirmed, and the testing and specialist routes available in the UK.

What it is and how it presents

Interpreting these tests is pattern work. A low C4 is the cheap, near-universal footprint of C1 inhibitor deficiency; adding level and function separates type 1 from the less common type 2, which normal-level assays alone would miss. Onset after 40 with low C1q raises acquired angioedema, which warrants a search for lymphoproliferative and autoimmune drivers. Meanwhile recurrent oestrogen-sensitive swelling with entirely normal complement may still be hereditary - the normal-C1-inhibitor HAE genes, led by F12.

Testing, surveillance and specialist care

Function assays are temperature-sensitive and need proper sample handling, so testing through an immunology service avoids false results, and borderline findings are repeated before labels are attached. SERPING1 sequencing confirms equivocal cases and drives family cascade testing with genetic counselling. NHS clinical genetics services carry some of the longest waits in the health service, often many months for a first appointment, whereas private genetic testing and a specialist review can typically be arranged within around two weeks.

Seeing a specialist

Who to see, and how quickly you can be seen.

The specialist for this condition is usually a immunologist. Your GP can refer you on the NHS, or you can arrange a private consultation directly.

A quiet reminder

This guide is for information, not medical advice.

Your GP knows your history and can tell you which parts apply to you. If in doubt, see them - and seek urgent care for any emergency symptoms.

Frequently asked

Common questions about C1 inhibitor testing.

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

  • What is c1 inhibitor testing?

    C1 inhibitor testing is a recognised medical condition that can affect people in different ways, ranging from mild and easily managed to more significant, depending on the underlying cause, how early it is picked up, and how it is treated. Getting a clear diagnosis is usually the first step towards the right management plan.

  • What causes c1 inhibitor testing?

    C1 inhibitor testing can arise from a combination of factors, which may include genetics, lifestyle, environmental exposures, other underlying health conditions, or simply the normal effects of ageing on the body. In many cases no single cause is found, and several factors act together. A clinician can help identify which factors are most relevant in an individual case.

  • What are the symptoms of c1 inhibitor testing?

    Symptoms of c1 inhibitor testing vary from person to person and depend on how severe the condition is and which structures are affected. Some people notice symptoms gradually over weeks or months, while others experience a more sudden onset. Because symptoms can overlap with other conditions, a proper assessment is important to reach an accurate diagnosis rather than relying on symptoms alone.

  • Is c1 inhibitor testing serious or dangerous?

    Most cases of c1 inhibitor testing are manageable, especially when identified and treated early, but severity varies from mild and self-limiting to more significant, depending on individual circumstances. Left unassessed, some cases can lead to complications or a longer-term impact on daily life. If you are worried about your symptoms, it is always worth getting them checked rather than waiting.

  • Is c1 inhibitor testing hereditary or genetic?

    Some cases of c1 inhibitor testing have a genetic component and can run in families, while others occur without any family history at all. Having a relative with the condition may modestly increase your own risk, but it does not mean you will definitely develop it yourself. If you are concerned about a family history, mention this to your doctor, as it may occasionally influence screening or monitoring.

  • Can c1 inhibitor testing be cured, reversed or prevented?

    Outlook varies with c1 inhibitor testing: some cases resolve completely with treatment, others improve significantly but need ongoing management, and a smaller number become a long-term condition to be controlled rather than cured. Prevention strategies, such as addressing modifiable risk factors, can reduce your chances of developing it or of it recurring, but cannot guarantee against it in every case.

  • How is c1 inhibitor testing treated?

    Treatment for c1 inhibitor testing is tailored to the individual and depends on severity, underlying cause and personal circumstances. Options can range from simple lifestyle measures, monitoring and conservative treatment through to medication, specialist procedures or surgery in more significant cases. A specialist assessment helps identify which combination of treatments is most appropriate for you.

  • How long does c1 inhibitor testing last?

    The duration of c1 inhibitor testing varies considerably: some people recover within days or weeks, while others live with a more persistent or recurring condition that needs ongoing management. Response to treatment, how early it is started, and individual factors all influence the timescale. Your clinician can give you a more personalised estimate once your specific circumstances are known.

  • When is surgery needed for c1 inhibitor testing?

    Surgery is not usually the first option for c1 inhibitor testing and is generally reserved for cases where conservative treatment has not worked, symptoms are severe, or there is a significant structural problem that needs to be corrected directly. The decision depends on your specific findings, symptoms and how they are affecting your life. A specialist consultation is the best way to establish whether surgery is being considered too early, or should be considered sooner rather than later.

  • When should I see a doctor about c1 inhibitor testing, and how quickly can I be seen privately?

    It is worth seeing a doctor about c1 inhibitor testing if symptoms are persistent, getting worse, or affecting your daily life, rather than waiting to see if they settle on their own. NHS routine referrals to a specialist can currently take anywhere from around 20 to 45 weeks or more depending on your area, whereas a private consultant can typically see you within about 2 weeks. Getting an earlier assessment can help clarify the diagnosis and start the right treatment sooner.