Pulmonary Embolism: Chest Infection Misdiagnosis Risk

Clinical Scenario

Danielle Foster, 29, has been directed to the GP by a pharmacist after requesting antibiotics for a 'chest infection.' She has had a dry cough, breathlessness, and right-sided pleuritic chest pain for 4 days. She was prescribed amoxicillin by an out-of-hours GP 2 days ago with no improvement. She returned from a long-haul flight from Australia 10 days ago. She is on the combined oral contraceptive pill. Her observations show a heart rate of 104, respiratory rate of 22, oxygen saturations of 94% on air, and temperature of 37.2°C. She thinks she just needs different antibiotics.

What This Case Tests

Recognising an atypical PE presentation misdiagnosed as a chest infection; identifying the risk factors for venous thromboembolism — long-haul flight plus combined oral contraceptive; applying the Wells score for PE; understanding that a low-grade temperature does not exclude PE; acting decisively to arrange same-day assessment; managing the patient's expectation that she needs different antibiotics

Common Mistakes Trainees Make

The three most common mistakes are: prescribing a different antibiotic because the first one did not work, without reconsidering the diagnosis — failure to respond to first-line antibiotics for a supposed chest infection should always prompt diagnostic reconsideration; being falsely reassured by the low-grade temperature and dry cough, which can occur in PE and do not confirm infection; and failing to calculate a Wells score or assess VTE risk factors, missing the long-haul flight and combined oral contraceptive as a significant risk factor combination.

The Consultation Challenge

Danielle believes she has a chest infection that needs stronger antibiotics. The pharmacist has directed her appropriately but has not identified the PE risk. You need to reassess from scratch.

Do not accept the previous diagnosis at face value. The key clinical reasoning trigger is: a young woman with pleuritic chest pain and breathlessness that has not responded to antibiotics. This should immediately prompt you to consider an alternative diagnosis.

Take a focused history: the pleuritic nature of the chest pain (sharp, worse on inspiration) is more typical of PE than infection. The dry cough is non-specific. Ask specifically about VTE risk factors: recent long-haul flight (10 days ago — within the high-risk window), combined oral contraceptive use (significant independent risk factor), any history of DVT or PE, family history of thromboembolism, any recent immobilisation, and any calf swelling or tenderness.

Review the observations: heart rate 104 (tachycardia), respiratory rate 22 (tachypnoea), oxygen saturations 94% (hypoxia for a 29-year-old). Temperature is only 37.2°C — this is borderline and does not confirm infection. These observations are more consistent with PE than chest infection.

Calculate the Wells score: clinical signs of DVT (check for calf swelling), PE is the most likely diagnosis (yes — 3 points), heart rate over 100 (yes — 1.5 points), recent immobilisation or surgery (the flight counts — 1.5 points). She is likely scoring at least 6, making PE probable.

Explain the clinical reasoning: 'Danielle, I have looked at everything carefully and I am concerned that this may not be a chest infection. The combination of your chest pain, breathlessness, the recent long-haul flight, and being on the pill raises the possibility of a blood clot on the lung — called a pulmonary embolism. Your observations support this concern. I need to send you to hospital today for a scan to check.'

Arrange same-day assessment: if clinically stable (which she is, with saturations of 94%), she can go to the acute medical unit or A&E by car with a companion. If unstable, call 999. Call ahead to the receiving team with a clear handover. If local protocols allow, arrange the CTPA request from primary care to expedite assessment.

Advise her to stop the combined oral contraceptive pill immediately. She should not fly again until investigated and cleared. If there will be a delay in hospital assessment, discuss whether empirical anticoagulation is appropriate per local guidelines.

Time check: Minutes 1-3 on reassessing the history and identifying VTE risk factors. Minutes 3-5 on reviewing observations and calculating Wells score. Minutes 5-8 on explaining the suspected diagnosis and arranging transfer. Minutes 8-10 on stopping the pill, advising against flying, and documentation.

How Examiners Mark This Case

Data Gathering and Diagnosis: Examiners assess whether you reconsider the diagnosis rather than accepting the previous assessment. Identifying the VTE risk factors (long-haul flight within 4 weeks, combined oral contraceptive), recognising that failure to respond to antibiotics should prompt diagnostic reconsideration, and interpreting the observations correctly (tachycardia, tachypnoea, hypoxia with only borderline temperature) are all essential. Calculating or referencing the Wells score demonstrates structured clinical reasoning.

Clinical Management and Medical Complexity: Examiners evaluate whether you arrange same-day hospital assessment, communicate effectively with the receiving team, stop the combined oral contraceptive, and advise against further flights. Knowing that CTPA is the investigation of choice and understanding the role of D-dimer in lower probability cases shows diagnostic depth. Considering empirical anticoagulation if there will be a delay demonstrates advanced management.

Relating to Others: Examiners look for how you shift the patient's understanding from 'I need different antibiotics' to 'I need to go to hospital today.' This requires clear, honest communication: explaining that the symptoms and risk factors point to something more serious than infection, without causing panic. Acknowledging that the previous GP may have been reasonable at the time but the picture has evolved shows professionalism.

Example Opening

Strong opening: "Hello Danielle, I understand the pharmacist sent you over. Rather than just switching your antibiotic, I want to start fresh and make sure we have the right diagnosis. Can you take me through exactly what you've been experiencing?"

When raising the PE concern: "Danielle, I've looked at the full picture — your symptoms, the fact the antibiotics haven't helped, the recent long-haul flight, and your observations — and I'm concerned this may not be a chest infection. There's a possibility this could be a blood clot on the lung, which is something that needs checking urgently. I want to send you to hospital today for a scan."

Avoid: "Let's try a different antibiotic and see how you go" — this delays diagnosis of a potentially fatal condition and represents a significant patient safety failure.

How This Appears in the SCA

This case tests your ability to reconsider a diagnosis when treatment has failed, identify VTE risk factors in a young woman, and apply clinical decision rules under pressure. Examiners value candidates who demonstrate diagnostic reasoning — explaining why this is not a chest infection and why PE is more likely — rather than simply following a protocol.

Key Statistic

Pulmonary embolism is the third most common cardiovascular cause of death. Approximately 25% of PE cases are initially misdiagnosed, most commonly as chest infection or musculoskeletal pain, contributing to delayed treatment and increased mortality.

Relevant Guidelines

• NICE NG158: Venous thromboembolic diseases — diagnosis, management and thrombophilia testing
• NICE CKS: Pulmonary embolism
• BTS guideline for the initial outpatient management of PE
• Wells score for PE.

Frequently Asked Questions

What are the key risk factors for pulmonary embolism in a young woman?

The major risk factors include: combined oral contraceptive pill use (increases VTE risk 3-4 fold), recent long-haul travel (flights over 4 hours, risk persists for up to 4 weeks), recent surgery or immobilisation, pregnancy or recent delivery, obesity, personal or family history of VTE, and thrombophilia. Danielle has two significant independent risk factors — the COCP and recent long-haul flight — which together create a multiplicative rather than additive risk increase. Always ask about these specifically in any young woman presenting with chest pain or breathlessness.

How do I use the Wells score for PE in primary care?

The Wells score assigns points for: clinical signs of DVT (3 points), PE is the most likely diagnosis (3 points), heart rate over 100 (1.5 points), immobilisation or surgery in the past 4 weeks (1.5 points), previous DVT or PE (1.5 points), haemoptysis (1 point), and active cancer (1 point). A score of 4 or below is 'PE unlikely' and D-dimer can be used to exclude; a score above 4 is 'PE likely' and requires imaging (CTPA) without waiting for D-dimer. In practice, if you clinically suspect PE, arrange urgent assessment — do not delay for investigations in primary care.

Why might PE be misdiagnosed as a chest infection?

PE and lower respiratory tract infection share several features: cough, breathlessness, pleuritic chest pain, and even low-grade fever. PE can cause a low-grade temperature through the inflammatory response. The key differentiating features are: PE typically causes a dry cough rather than productive, the chest pain is sharply pleuritic, tachycardia is often disproportionate to the fever, and there are identifiable VTE risk factors. Failure to respond to antibiotics within 48-72 hours should always prompt diagnostic reconsideration.

Should I stop the combined oral contraceptive pill immediately?

Yes. If PE is suspected, the COCP should be stopped immediately and not restarted until VTE has been excluded by investigation. If PE is confirmed, the COCP is permanently contraindicated and the patient will need alternative contraception. Offer a progesterone-only method (POP, implant, or hormonal IUS) as these do not carry the same VTE risk. The patient should be counselled that she may need lifelong avoidance of oestrogen-containing contraception depending on the outcome of thrombophilia testing.

When can I safely use D-dimer to exclude PE in primary care?

D-dimer can only be used to exclude PE when the pre-test probability is low — a Wells score of 4 or below. A negative D-dimer in a low-probability patient effectively excludes PE with a negative predictive value exceeding 99%. However, D-dimer should never be used when clinical probability is moderate or high (Wells above 4) because a negative result is insufficiently reliable to exclude PE. In Danielle's case, her Wells score is likely above 4, so D-dimer would not be appropriate — she needs direct imaging with CTPA.