How to Write a Letter to a Hospital About a Missed Diagnosis UK: A Complete Guide

R

A missed diagnosis can cause serious, sometimes irreversible harm. Treatment delayed because a condition was not identified, a cancer not caught at an early stage, a serious illness dismissed as something minor. When that happens, you have every right to ask the hospital for an explanation, to raise a formal complaint and, where appropriate, to seek a legal remedy.

Writing to the hospital is the right first step. It creates a documented record, triggers the hospital’s formal complaints obligations, and often produces information you could not get any other way. It also starts the clock on timescales that matter if you later want to escalate to the Parliamentary and Health Service Ombudsman or seek legal advice about a clinical negligence claim.

This guide explains what a missed diagnosis complaint involves, what to include in your letter, how the NHS complaints process works, and what your options are if the hospital’s response does not provide what you need.

What Counts as a Missed Diagnosis

A missed diagnosis means that a condition was present but not identified when it should have been. This can happen in several ways. The symptoms may have been present but not investigated appropriately. Tests may have been ordered but not followed up or the results not communicated. A referral may not have been made when it should have been. A diagnosis may have been made but the wrong one, meaning the actual condition went untreated.

Not every missed diagnosis amounts to negligence or to a complaint that will be upheld. Medicine involves clinical judgment and not every condition is straightforward to identify. What a complaint addresses is whether the hospital or its clinicians fell below the standard of care that a reasonably competent doctor in their position would have provided. If your condition was one that should have been diagnosed earlier given the symptoms and investigations available, and if the delay caused you harm, a complaint is justified.

Important: A complaint to the hospital and a clinical negligence claim are two separate processes. A complaint seeks an explanation, an apology and learning. A negligence claim seeks compensation. You can pursue both, and in some cases the hospital’s response to your complaint will inform any legal advice you take. But they follow different timescales and involve different organisations.

Before You Write: What to Prepare

A complaint about a missed diagnosis is more complex than most other NHS complaints because it involves clinical judgment. Preparing properly before you write gives the complaint the best chance of being investigated thoroughly.

• Write out a clear timeline of events: every appointment, every test, every consultation, every symptom you reported, and every response you received from clinical staff.

• Gather all documentation you have: appointment letters, discharge summaries, test results, any written communication from the hospital.

• Request your medical records if you do not already have them. You are legally entitled to a copy of your records under the UK GDPR. The hospital must provide them within one month. Having the records before you write means you can reference specific entries and identify where the failure occurred.

• Note the impact clearly: what happened as a result of the missed diagnosis, how your treatment or prognosis changed, what procedures or treatments you have had to undergo that might have been avoided, and any lasting effects on your health or daily life.

• Consider whether you want independent medical advice before writing. For complex clinical complaints, a specialist medical opinion can strengthen your understanding of where care fell below the expected standard.

Tip: You can request your medical records by writing to the hospital’s medical records department or data protection officer. State that you are making a Subject Access Request under the UK GDPR and ask for all records held in relation to your care. There should be no charge for this request.

The NHS Complaints Process: How It Works

All NHS hospitals in England are required to operate a complaints process under the NHS Complaint Standards, which are set and monitored by the Parliamentary and Health Service Ombudsman. Every complaint must be acknowledged within three working days. A full response must be provided within the agreed timescale, which should be discussed with you at the outset. For complex clinical complaints, this is often between 25 and 40 working days, though it can be longer. The hospital should keep you informed if it needs more time.

Before or instead of making a formal complaint, you can contact the hospital’s Patient Advice and Liaison Service, known as PALS. PALS is a free, confidential service available in most NHS hospitals that can help you raise concerns informally and may be able to resolve straightforward issues without a formal complaint. For a missed diagnosis complaint involving significant harm, PALS is unlikely to provide the level of investigation you need, but it can be a useful first contact to understand the process and identify who to write to.

You can find your hospital’s PALS contact details on the NHS website PALS finder or by asking the hospital reception directly.

Who to Address Your Complaint To

Address your formal complaint letter to the Chief Executive of the NHS Trust responsible for the hospital, or to the Patient Experience or Complaints Manager. The Chief Executive is ultimately accountable for the quality of care provided by the Trust and addressing your letter to them signals the seriousness of the complaint. In practice, the letter will usually be handled by the complaints team, but copying or addressing the Chief Executive ensures it is treated at the appropriate level.

You can find the name and address of the Chief Executive on the Trust’s website, usually in the leadership or contact section. If you are not sure which Trust is responsible for the hospital, check the NHS website.

What to Include in Your Letter

Opening: State This Is a Formal Complaint

Use those words in the subject line and opening sentence. This is not optional. It determines how the letter is logged and triggers the hospital’s formal obligations.

Your Details and the Patient’s Details

Include your full name, address and contact details. If you are writing on behalf of someone else, state your relationship and confirm you have their consent. Include the patient’s full name, date of birth, NHS number if you have it, and the hospital and department involved.

The Background: A Clear Chronology

Set out the events in chronological order. Describe each appointment or contact with the hospital, what symptoms or concerns you reported, what investigations or tests were carried out and when, what you were told and by whom, and what happened as a result. Be specific about dates. Reference specific documents where you have them.

What You Say Went Wrong

State clearly what you believe the hospital failed to do and when. This might be a failure to investigate reported symptoms, a failure to follow up on test results, a failure to make a timely referral, or a failure to diagnose a condition that the clinical picture should have raised. Be specific and factual. Avoid general expressions of dissatisfaction. Refer to specific appointments, specific symptoms reported and specific responses received.

The Impact

Describe what the missed diagnosis has cost you. A later-stage diagnosis that required more aggressive treatment than would have been needed earlier. A period of illness that was untreated and worsened. Permanent damage that might have been avoided. Lost time from work. The effect on your family. Be honest and specific. The hospital needs to understand the full picture of harm to respond appropriately and to consider what remedy is appropriate.

What You Are Asking For

State clearly what you want from the complaint. Most people want four things: a full explanation of what happened and why, an acknowledgment of what went wrong, an apology if fault is found, and confirmation of what steps the hospital has taken or will take to prevent the same thing happening to someone else. If you are seeking a financial remedy at this stage, include that request, though clinical negligence compensation is generally pursued through a separate legal process.

Full Worked Example

[Your name]

[Your address]

[Your email and telephone]

[Date]

[Chief Executive name]

[NHS Trust name]

[Trust address]

Subject: Formal Complaint – Missed Diagnosis of [Condition] – [Your name], DOB [date], NHS number [number]

Dear [Name],

I am writing to make a formal complaint about the care I received at [hospital name], under the [department] team, between [dates]. I believe that a diagnosis of [condition] was missed over a period of [timeframe], resulting in significant harm that I will set out below.

Background

On [date] I attended [hospital / department] with the following symptoms: [describe clearly]. I was seen by [describe the clinician if known, e.g. a registrar in the respiratory team] and was told [describe what you were told]. No further investigations were arranged at that point.

On [date] I returned to [hospital / GP / A&E] with [describe symptoms, noting any change or worsening]. I was again told [what you were told] and [describe what happened or did not happen: no referral was made / the test results were not reviewed / I was discharged without investigation].

On [date], [describe how the correct diagnosis was eventually made: I was seen by a different clinician / I sought a private opinion / I attended A&E with acute symptoms]. I was diagnosed with [condition]. I was told that [describe anything you were told about how long the condition had been present or about what earlier intervention would have meant for your treatment or prognosis].

What I believe went wrong

I believe the hospital failed to diagnose my condition in a timely manner for the following reasons. First, the symptoms I described on [date] and [date] were consistent with [condition] and, in my understanding, should have prompted further investigation at an earlier stage. Second, [describe any specific failure: the test results from [date] showed [finding] which I understand should have prompted a referral that was not made / I was not referred to a specialist despite reporting symptoms on multiple occasions over [timeframe]]. Third, [describe any further failure if relevant].

Impact

As a result of the delayed diagnosis, I have experienced the following: [describe the impact clearly, e.g. my condition had progressed to stage [X] by the time it was diagnosed, requiring [more extensive treatment] rather than the [less invasive treatment] that would have been available at an earlier stage / I suffered [specific health consequences] that my specialist has told me were directly related to the delay / I have been unable to work since [date] as a result of the treatment I have required].

What I am asking for

I am asking the Trust to: provide me with a full explanation of the clinical decisions made at each stage of my care and the reasons why a diagnosis was not reached earlier; acknowledge whether the standard of care I received fell below what I should have expected; if fault is found, provide me with a formal written apology; and explain what steps the Trust has taken or will take to ensure a similar failure does not occur in future.

I would like to receive the response within the timescale agreed with me at acknowledgement. If the investigation is likely to take longer than 30 working days, please advise me of the revised timescale and the reasons for it.

I am happy to provide any further information, including a copy of my medical records if needed, to assist the investigation.

Yours sincerely,

[Your name]

[Signature]

The Duty of Candour

Under the statutory Duty of Candour, which applies to all NHS providers, hospitals are legally required to be open and transparent with patients when something goes wrong with their care that has caused, or could cause, harm. If your missed diagnosis resulted in moderate or severe harm, the hospital should have told you at the time it became aware of the failure. If they did not, you can raise the failure to comply with the Duty of Candour as an additional ground in your complaint. The NHS England guidance on the Duty of Candour sets out what patients are entitled to expect.

If the Hospital’s Response Is Inadequate

If the hospital provides a response that does not address your complaint fully, denies fault without adequate explanation, or fails to respond within the agreed timescale, you have two main escalation routes.

The Parliamentary and Health Service Ombudsman

The Parliamentary and Health Service Ombudsman is the independent body that investigates unresolved NHS complaints in England. You can approach the Ombudsman once you have received the hospital’s final response, or if the hospital has not responded within a reasonable time. The Ombudsman’s service is free. If the Ombudsman upholds your complaint, it can recommend that the hospital apologises, provides you with a financial remedy, or makes changes to its practices. The Ombudsman now focuses on the more serious cases where there is significant impact on the complainant.

You must submit your complaint to the Ombudsman within 12 months of becoming aware of the issue you are complaining about, though this time limit can be waived in exceptional circumstances. Do not delay once you have received the hospital’s final response.

Clinical Negligence: When to Take Legal Advice

If the missed diagnosis caused you significant harm and you believe the hospital’s care fell below the standard expected of a reasonably competent clinician, you may have a clinical negligence claim. Clinical negligence claims are separate from the complaints process and involve demonstrating both that care fell below the required standard and that this caused your injury or worsened your condition.

The time limit for bringing a clinical negligence claim in England is generally three years from the date you were injured, or three years from the date you became aware that the injury was caused by the medical care you received. This is known as the limitation period and it is strictly applied. If you are considering a legal claim, seek advice from a specialist clinical negligence solicitor as early as possible. Many operate on a no-win no-fee basis for cases with merit.

Free initial guidance on clinical negligence is available from AvMA (Action against Medical Accidents), a specialist charity that provides free advice and can help you identify whether your situation warrants a legal claim. Their helpline is 0345 123 2352. Citizens Advice also provides guidance on the NHS complaints process and signposting to further help.

Getting Help With Your Letter

A complaint about a missed diagnosis is one of the most significant letters you are likely to write to an NHS organisation. If you find the process difficult or want support in structuring your complaint, free help is available from several sources.

NHS complaints advocacy services offer free, independent support in writing your complaint and attending meetings. NHS England’s guidance on complaints advocacy explains how to access this service. AvMA also provides specialist support for medical complaints involving harm. For complex cases where the clinical issues require expert assessment, a clinical negligence solicitor can often provide an initial consultation at no cost.

If you want help drafting a clearly structured, precisely worded complaint letter before you send it, the team at LetterLab can help you ensure the letter covers the right ground, references the key points and is presented in a way that is most likely to prompt a thorough investigation.

Checklist: Before You Send Your Letter

1. Have you obtained a copy of your medical records before writing?

2. Does the subject line and opening sentence state this is a formal complaint?

3. Is it addressed to the Chief Executive or Complaints Manager of the correct NHS Trust?

4. Have you set out the events in chronological order with specific dates?

5. Have you clearly identified what you say went wrong and at which point?

6. Have you described the impact on your health, treatment and daily life specifically?

7. Have you stated clearly what outcome you are seeking?

8. Have you asked for a response within an agreed timescale?

9. Have you sent the letter by recorded post or email with read receipt and kept a copy?

10. If the delay in diagnosis may give rise to a legal claim, have you noted the three-year limitation period and considered taking early legal advice?

The Key Takeaway: Write It Formally, Describe the Harm, Follow the Process Through

A missed diagnosis complaint is serious and it deserves to be treated seriously. The hospital has an obligation to investigate it properly, to explain what happened and why, and to acknowledge any failure. The NHS complaints process exists for exactly this purpose and, when used correctly, it can produce the explanation and accountability that a verbal conversation never will.

Write the letter carefully. Be specific about what happened and when. Describe the harm clearly. Ask for the explanation and acknowledgement you are entitled to. Then, if the response is not adequate, use the escalation routes available. The Ombudsman, the Duty of Candour and, where appropriate, the courts, all exist to ensure that patients who are harmed by substandard care are not simply left with nothing.