Red flags in clinical practice: expert insights on delayed diagnosis and patient harm

In my work as a clinical negligence solicitor, I regularly act for clients where a serious condition was not identified at the earliest opportunity. 

By Rachel Makore, Associate Clinical Negligence Solicitor

A common feature in many of these cases is not a lack of clinical knowledge, but a failure to recognise, properly weigh, or act on key features in a patient’s presentation.

This article forms part of our “Red flags in clinical practice” series, where frontline clinicians share insights into recognising time-critical conditions and understanding how delays in diagnosis can occur.

By exploring these issues from a clinical perspective, alongside the medico-legal context in which they often arise, the aim is to provide a clearer understanding of how delays in diagnosis occur and the very real consequences they can have for patients.

In this first article, Senior Charge Nurse Oluwafemi Oni shares his perspective from the frontline of A&E practice, focusing on subarachnoid haemorrhage.

Frontline Failures: An A&E Expert's View on Subarachnoid Haemorrhage

By Oluwafemi Oni, RN, BSc (Hons), MBA — Senior Charge Nurse, NHS Accident & Emergency

Introduction

I qualified as a Registered Nurse in 2016, and I am currently a Senior Charge Nurse in a busy NHS Accident & Emergency Department. I lead a multidisciplinary team caring for both adult and paediatric patients. My role includes triage, rapid assessment, resuscitation, and escalating deteriorating patients to the appropriate clinical team.
Alongside my clinical role, I work as an expert witness with Somek and Associates and accept instructions from both claimant and defendant solicitors. The two roles feed into each other. Working on the clinical floor allows me to see how things can actually go wrong; reviewing cases tells me how frequently these patterns repeat. What I see, again and again, is that missed cases of subarachnoid haemorrhage rarely come down to a gap in clinical knowledge. They come down to red flags being there in the history, but not being recognised, not acted on, or not properly documented under the pressures of a busy department.

What is a subarachnoid haemorrhage (SAH)?

Subarachnoid haemorrhage is a serious, time-critical bleed around the brain, most often caused by a ruptured aneurysm. It is not the most common cause of headache we see in A&E, but it is one of the most important not to miss. Published emergency medicine literature reports missed diagnosis rates anywhere from 12% to 51%.

Key red flags for subarachnoid haemorrhage

1. The thunderclap headache. NICE defines SAH as a cause of acute headache that reaches maximum intensity within minutes. Patients often describe it as the worst headache of my life. This is the single most important historical feature, and the one that gets dismissed most often, especially when the patient looks well by the time they reach the point of assessment. It gets missed because it can mimic tension headache or migraine, because patients struggle to pin down the precise onset, and because once analgesia has taken effect, the urgency of the original presentation quietly fades from the picture.
2. Transient loss of consciousness or collapse at onset. A patient who briefly loses consciousness with a severe headache and then recovers fully is a real diagnostic trap. The temptation is to put the collapse down to a vasovagal episode, a seizure, or something cardiac, particularly when the observations are normal and the ECG is unremarkable. Quick recovery breeds false reassurance. Without a clear collateral history, the significance of the original event is easily lost.
3. Associated red flag features. Neck stiffness, vomiting, reduced level of consciousness, seizures, or any focal neurological deficit should all push suspicion up. These are well known. The problem isn't that we don't recognise them in isolation, it is that under pressure they get documented individually rather than pulled together into a coherent clinical picture.
4. Deviation from the patient's baseline headache pattern. A patient with a long history of migraines who tells you this one is different, different in onset, different in character, different in severity, needs a fresh diagnostic approach, not reassurance based on their past medical history.
5. A normal neurological examination. This is probably the most dangerous trap of all. Early or limited haemorrhage can be present in a patient who is fully conscious, fully oriented, and neurologically pristine. A normal exam does not exclude SAH. It should never be the basis for discharge when the history contains concerning features.

Why SAH is often missed in A&E

The clinical features themselves are well taught. What fails, in my experience, is the integration of those features under pressure. Cognitive bias plays a significant role.

Once a working diagnosis of migraine or tension headache forms, the rest of the information gets filtered through that lens. This is premature diagnostic closure, and from a medico-legal perspective it is a recurring root cause when red flags are missed. Add incomplete history-taking, no collateral, false reassurance from normal observations, and the constant pressure to see, treat, and discharge or admit patients within four hours, and the conditions for a missed diagnosis are all there.

When does a missed diagnosis become negligence?

Clinically, the question is: could this be SAH? Medico-legally, the question is: did the assessment meet the standard expected of a reasonably competent clinician at that level? The two are closely linked. NICE guidance is clear. The red flags for SAH are well established in national standards and in emergency care training. Where a thunderclap headache is documented but not investigated, or a patient is discharged with a documented history of collapse and sudden severe headache without imaging or senior review, the decision-making may fall below the expected standard. In those circumstances, a delay in diagnosis can amount to a breach of duty, and where that delay causes avoidable harm, it can give rise to a claim in clinical negligence.

Case example: delayed diagnosis of SAH

A woman in her 40s arrives at A&E with a sudden severe headache that woke her from sleep. She vomited once. No past medical history of note. Observations stable. By the time she is seen, paracetamol has taken the edge off. Neurological examination is normal. She's reassured, given a migraine diagnosis, and discharged with safety-netting advice. Forty-eight hours later she re-presents with reduced consciousness and a confirmed SAH on CT.

The error is not in the examination; that was done competently. The error is in letting a normal examination and a settled patient override a textbook thunderclap history.

Safety-netting is not a substitute for acting on red flags at the point of first presentation.

If I could change one thing...

History must always take precedence over examination findings. A reassuring neurological exam, stable observations, and a settled patient should never close the diagnostic door on a sudden-onset severe headache. The threshold for urgent CT and senior review in these presentations should be low. The decision not to image a patient with a thunderclap history should be the one that needs justification, not the other way around.

Contact Dean Wilson LLP 

If you or a loved one has experienced a delay in the diagnosis of a subarachnoid haemorrhage and have concerns about the care received, our clinical negligence team would be happy to offer initial guidance. Please contact us on 01273 249200 or visit our Medical Negligence page for further information.