Shortness of breath differential diagnosis (dyspnoea)

Shortness of breath is a symptom with a short list of common causes and a long tail of rare ones. In roughly two thirds of patients presenting with dyspnoea the underlying cause is cardiopulmonary disease, and asthma, heart failure, COPD, pneumonia, cardiac ischaemia, interstitial lung disease and psychogenic causes together account for 85% of cases (Karnani et al., American Family Physician 2005). The differential is therefore best worked in a fixed order: decide whether the patient is stable, exclude the time-critical causes, then separate acute from chronic breathlessness and use base rates to rank what remains.

This is a working reference for clinicians. It covers how to structure the differential, the red flags that override everything else, which diagnoses are actually most common, how acute and chronic presentations diverge, how to separate cardiac from respiratory breathlessness at the bedside, the staged workup, when to think pulmonary embolism, and the causes that sit outside the heart and lungs. Dyspnoea is defined by the American Thoracic Society as "a subjective experience of breathing discomfort that comprises qualitative distinct sensations", and is called chronic when it has been present for more than one month (Budhwar and Syed, American Family Physician 2020).

Key takeaways

• Dyspnoea accounts for up to 2.5% of all family physician visits and up to 8.4% of emergency-department visits (AAFP 2020).
• Two thirds of cases are cardiopulmonary, and seven diagnoses explain 85% of patients whose main complaint is breathlessness (AAFP 2005). Asthma, COPD, heart failure, pneumonia and coronary artery disease alone account for nearly 85% of underlying aetiologies (AAFP 2020).
• The findings that reorder the whole plan are hypotension, altered mental status, hypoxia and unstable arrhythmia — plus stridor with respiratory effort but no air movement, and unilateral tracheal deviation with unilateral breath sounds and hypotension (AAFP 2003).
• Timing is diagnostic. Sudden breathlessness at rest suggests pulmonary embolism or pneumothorax; severe distress continuing over one to two hours suggests heart failure or asthma (AAFP 2003).
• History carries the diagnosis in at least half of patients, and history, examination and chest radiography were 81% accurate for the four commonest diagnoses (AAFP 2005).
• First-line testing is pulse oximetry, full blood count, basic chemistry, ECG, chest radiography and spirometry, ordered in stages (AAFP 2020).
• COPD is not a clinical diagnosis: it requires spirometry showing a post-bronchodilator FEV1/FVC ratio below 0.7 (AAFP 2023).
• Dyspnoea itself predicts death. Patients presenting to an emergency department with dyspnoea had 1.37-fold greater 10-year mortality than the general population (AAFP 2020).

What is the differential diagnosis of shortness of breath?

The differential for shortness of breath is organised by system, not by symptom description. Pulmonary and cardiac disease account for about two thirds of presentations; the remaining third is haematological, metabolic, neuromuscular, endocrine, musculoskeletal or psychological. Deconditioning, obesity and pregnancy are common and frequently missed contributors rather than diagnoses of exclusion.

The AAFP's 2020 review groups chronic dyspnoea as follows, and the same architecture works for acute presentations once the emergencies have been excluded:

• Pulmonary — obstructive (COPD, asthma), alveolar (recurrent pneumonia), interstitial (idiopathic pulmonary fibrosis), restrictive (pleural effusion) and vascular (chronic pulmonary emboli).
• Cardiac — heart failure, arrhythmia (for example atrial fibrillation), valvular disease (for example aortic stenosis), pericardial disease and cardiac tumours.
• Haematological — anaemia.
• Endocrine and metabolic — hypothyroidism, metabolic acidosis including diabetic ketoacidosis.
• Neuromuscular — respiratory muscle weakness, for example phrenic nerve palsy.
• Musculoskeletal — chest wall deformity such as kyphosis.
• Gastrointestinal — aspiration from gastro-oesophageal reflux.
• Psychological — anxiety, which the AAFP treats explicitly as a diagnosis of exclusion.
• Physiological and other — obesity, deconditioning, pregnancy, medication effects.

Two framing points matter before any test is ordered. First, the AAFP states plainly that "despite its pervasiveness in clinical medicine, there is no standardized approach for evaluating chronic dyspnea" — so the structure you bring is your own. Second, breathlessness in older adults is frequently multifactorial: around 30% of people over 65 report some difficulty breathing while walking, and in one community sample of people over 70 the prevalence was 32% (AAFP 2020). Finding one cause does not mean you have found the only one. The same reasoning discipline applies across symptoms; we set out the general method in what is a differential diagnosis?

What are the red flags in acute breathlessness?

Four findings mark an unstable patient who needs resuscitation before diagnosis: hypotension, altered mental status, hypoxia and unstable arrhythmia (AAFP 2003). Two bedside patterns point to specific emergencies: stridor with visible respiratory effort but no air movement suggests upper airway obstruction, and unilateral tracheal deviation with unilateral breath sounds and hypotension suggests tension pneumothorax.

The AAFP's 2003 office review also flags a respiratory rate above 40 breaths per minute, retractions, cyanosis and low oxygen saturation as signs of impending failure. None of these is a diagnosis; each is an instruction to secure the airway, give oxygen and escalate while the differential continues in parallel.

Which causes of shortness of breath are most common?

Five diagnoses dominate. Asthma, COPD, heart failure, pneumonia and coronary artery disease account for nearly 85% of underlying aetiologies of dyspnoea (AAFP 2020). Adding interstitial lung disease and psychogenic causes to that list gives the 85% figure reported for patients whose principal symptom is breathlessness (AAFP 2005).

The global burden behind those labels is substantial. The World Health Organization estimates that asthma affected 363 million people in 2023 and caused 442,000 deaths, with most asthma deaths occurring in low- and lower-middle-income countries (WHO asthma fact sheet). COPD is the third leading cause of death worldwide, causing 3.4 million deaths in 2023, and nearly 90% of COPD deaths in people under 70 occur in low- and middle-income countries (WHO COPD fact sheet). Anaemia — which the WHO lists as causing shortness of breath alongside fatigue and reduced physical work capacity — affects an estimated half a billion women aged 15 to 49 and 269 million children aged 6 to 59 months (WHO anaemia fact sheet).

There is a useful second list for the patient who defeats the first pass. In one study of patients whose dyspnoea was unexplained by history, examination, chest radiography and spirometry, the commonest eventual causes were COPD, congestive heart failure, psychogenic causes and deconditioning (AAFP 2005). In other words, the common things stay common even after the obvious tests come back normal — a normal chest film does not move COPD or heart failure down the list.

How does acute dyspnoea differ from chronic dyspnoea?

The threshold is one month: dyspnoea present for longer than that is chronic (AAFP 2020). The distinction changes the whole approach. Acute breathlessness is a stability and exclusion problem worked in minutes; chronic breathlessness is a staged-testing problem worked over visits, where the yield comes from history and sequencing rather than speed.

Within acute presentations, the tempo itself discriminates. Sudden shortness of breath at rest is suggestive of pulmonary embolism or pneumothorax, while severe respiratory distress continuing over one to two hours suggests congestive heart failure or asthma (AAFP 2003). Ask when it started, what the patient was doing, and whether it has plateaued or is still worsening — three questions that do more diagnostic work than most initial tests.

For chronic dyspnoea, symptom severity should be graded rather than described. The Modified Medical Research Council Dyspnea Scale or the COPD Assessment Test can be used to assess symptom severity (AAFP 2023), and the New York Heart Association classification is the simplest and most widely used method to gauge symptom severity in heart failure — and is itself a well-established predictor of mortality (King et al., American Family Physician 2012). A graded baseline is what makes the next review interpretable.

How do you tell cardiac from respiratory breathlessness?

History does most of the work: in at least half of patients the diagnosis can be made on the history alone, and history, examination and chest radiography together were 81% accurate for the four commonest diagnoses (AAFP 2005). At the bedside, a small number of signs are highly specific for heart failure, and a small number of tests separate obstructive from restrictive lung disease.

On the cardiac side, nearly all patients with heart failure have dyspnoea on exertion, and several examination and radiographic findings are strikingly specific even though they are insensitive: a third heart sound (specificity 0.99), interstitial oedema on chest radiography (0.97), hepatojugular reflux (0.96), a displaced cardiac apex (0.95) and jugular venous distension (0.92). Orthopnoea and paroxysmal nocturnal dyspnoea, by contrast, have only a small effect on probability (AAFP 2012, heart failure). The practical reading: these signs are for ruling in, not ruling out.

Natriuretic peptides work the other way round. Systolic heart failure can be effectively ruled out with a normal B-type natriuretic peptide or NT-proBNP level (AAFP 2012, heart failure), and at a threshold of 100 pg/mL BNP was 82% sensitive and 99% specific in the AAFP's 2005 review. The important exception is preserved ejection fraction: up to 29% of patients with confirmed heart failure with preserved ejection fraction have a normal BNP, most often patients younger than 50 and those with obesity, while levels may be higher in patients older than 75 (AAFP 2020). Echocardiography remains the diagnostic standard to confirm systolic or diastolic heart failure (AAFP 2012, heart failure) and the test of choice for most cardiac causes of chronic dyspnoea (AAFP 2005).

On the respiratory side, spirometry indicates obstructive airway disease when the FEV1 or the FEV1/FVC ratio is low, but restrictive disease requires lung volume measurement to confirm (AAFP 2020). COPD specifically requires spirometry showing a post-bronchodilator FEV1/FVC ratio below 0.7; the AAFP is explicit that "COPD is not diagnosed clinically" and that relying on symptoms without performing spirometry increases the risk of misdiagnosis (AAFP 2023). That is a global access problem as much as a clinical one: the WHO notes that in low- and middle-income countries spirometry is often not available and so the diagnosis may be missed.

Two physical signs earn their place. Pulsus paradoxus — a fall of more than 10 mmHg in systolic pressure during inspiration — is associated with severe COPD, asthma, large pleural effusions, pulmonary embolism and subacute tamponade. Nail clubbing should prompt evaluation for lung cancer, lung abscess, bronchiectasis or idiopathic pulmonary fibrosis (AAFP 2020).

What is the first-line workup for shortness of breath?

Initial testing should include pulse oximetry, a full blood count, a basic chemistry panel, electrocardiography, chest radiography and spirometry, ordered in stages rather than all at once; thyroid function testing is also reasonable in the initial panel (AAFP 2020). In the acute office setting the core four are pulse oximetry, full blood count, electrocardiography and chest radiography (AAFP 2003).

The AAFP's 2020 review sequences the workup in three tiers, and its recommendations for chronic dyspnoea carry SORT level C evidence — consensus and usual practice rather than trial data, which is itself worth knowing:

• First tier — pulse oximetry, full blood count, chemistry panel, ECG, chest radiography, spirometry, thyroid function.
• Second tier (non-invasive) — echocardiography, cardiac stress testing, full pulmonary function tests, chest CT. High-resolution non-contrast chest CT should be performed if the diagnosis of dyspnoea remains unclear — and a pulmonary aetiology is suspected; the AAFP qualifies the recommendation on both counts.
• Third tier (invasive, with specialist input) — bronchoscopy, lung biopsy, cardiac catheterisation.
• Targeted additions — ECG, BNP and cardiac ultrasonography if heart failure is suspected; chest radiography followed by spirometry if a pulmonary cause is suspected; cardiopulmonary exercise testing where dyspnoea seems out of proportion to the known cardiac or pulmonary disease.

One non-test intervention belongs in the same list: smoking history and exposure should be assessed and cessation encouraged regardless of how long the patient has smoked (AAFP 2020). Tobacco use is the largest risk factor for COPD (AAFP 2023), accounting for over 70% of cases in high-income countries and 30–40% in low- and middle-income countries, where household air pollution is a major risk factor (WHO).

When should you suspect pulmonary embolism?

Suspect pulmonary embolism when breathlessness is sudden and at rest, and especially when it is accompanied by pleuritic chest pain: dyspnoea or tachypnoea with pleuritic chest pain occurs in 97% of patients who have clinically apparent pulmonary embolism (AAFP 2003). Assessment then runs on pretest probability, not on the D-dimer result alone.

The Wells rule has been widely validated and is commonly used to assign pretest probability, stratifying patients as low (score below 2), intermediate (2 to 6) or high (7 or more); no single rule has been proven superior (Wilbur and Shian, American Family Physician 2012). From there:

• Low pretest probability plus a negative D-dimer excludes pulmonary embolism, and no further workup is necessary. High-sensitivity D-dimer assays are more than 95% sensitive for venous thromboembolism with a negative predictive value of about 94%.
• With intermediate-to-high pretest probability, a D-dimer should not be performed initially, because a negative result cannot safely exclude venous thromboembolism.
• Multidetector CT angiography is the diagnostic test of choice where available and appropriate, and may be used first in high-probability patients regardless of D-dimer.
• A negative CT angiogram does not settle it when clinical probability is high. The positive predictive value of CT angiography is 92–96% in intermediate-to-high-risk patients, but the negative predictive value is only 60% in high-clinical-probability patients — it cannot reliably exclude pulmonary embolism in that group.
• Positive D-dimer results are not diagnostic: impaired renal function, ongoing blood loss, pregnancy and atrial fibrillation all raise levels.

Two other diagnoses deserve a named place in the acute differential. Paroxysmal dyspnoea or pulmonary oedema may be the only clinical presentation in 10% of patients with myocardial infarction — breathlessness without chest pain does not exclude an infarct, which is why the chest pain differential diagnosis and the dyspnoea differential overlap so heavily. And in spontaneous pneumothorax, chest pain is almost universal while dyspnoea is the second most common symptom (AAFP 2003).

What causes breathlessness outside the heart and lungs?

About a third of presentations are not cardiopulmonary. The highest-yield non-cardiopulmonary causes are anaemia, metabolic acidosis, hypothyroidism, respiratory muscle weakness, chest wall deformity, deconditioning, obesity, pregnancy, medication effects and anxiety — the last of which the AAFP treats as a diagnosis of exclusion rather than a first impression (AAFP 2020, AAFP 2003).

Anaemia is the one most worth a reflex test, because it is common, cheap to detect and listed by the WHO as a direct cause of shortness of breath, particularly on exertion. It is also why the full blood count sits in the first tier alongside the chest film. Metabolic causes, including diabetic ketoacidosis and salicylate toxicity, present as tachypnoea rather than true air hunger and are easy to mislabel as anxiety in a distressed patient. Medication review matters for the same reason — and interacting drugs can produce or worsen breathlessness, which we cover in the drug interactions guide.

A worked example (illustrative)

A 58-year-old with a 30-pack-year smoking history reports six months of breathlessness on climbing stairs, now at one flight. No orthopnoea, no chest pain, no fever. Observations are normal apart from oxygen saturation of 94% on air. This is chronic dyspnoea by definition, and the pretest differential is dominated by COPD, heart failure and deconditioning.

First tier: full blood count (anaemia), chemistry, ECG, chest radiography, spirometry, pulse oximetry, thyroid function. A graded severity score is recorded at this visit so the next one is comparable. If spirometry shows a post-bronchodilator FEV1/FVC below 0.7, COPD is confirmed — not assumed from the smoking history. If spirometry is normal, heart failure has not been excluded: BNP and echocardiography are the next step, and a normal BNP would be reassuring for systolic failure but not for preserved ejection fraction in a patient with obesity. If both tiers are unrevealing and a pulmonary aetiology is still suspected, high-resolution non-contrast chest CT is indicated, with cardiopulmonary exercise testing where breathlessness seems disproportionate to the findings. Deconditioning remains on the list throughout, and it is the diagnosis most often reached by exclusion.

This example is illustrative and not a substitute for assessment of a real patient or for local guidelines.

Where decision support fits

Breathlessness is a good test of decision support because the failure mode is sequencing, not knowledge: the five common causes are known to everyone, the dangerous ones are time-critical, and the workup is explicitly unstandardised. Shifaa AI — an AI clinical assistant currently in private beta — is built for that gap. Its differential-diagnosis support surfaces a ranked differential, raises the red-flag presentations ahead of the likely ones, and shows the guidance behind each suggestion so you can check it. It is decision support: it does not diagnose, and the clinician reviews, edits and signs, as we argue in can AI diagnose patients? Because the reasoning has to survive into the record, the assessment and plan are where it has to land cleanly — our free SOAP note template is built around exactly that.

For the neighbouring symptom references, see the headache differential diagnosis and the abdominal pain differential diagnosis by location.

Frequently asked questions

What are the red flags for shortness of breath?

Hypotension, altered mental status, hypoxia and unstable arrhythmia mark an unstable patient who needs resuscitation before diagnosis. Stridor with respiratory effort but no air movement suggests upper airway obstruction, and unilateral tracheal deviation with unilateral breath sounds and hypotension suggests tension pneumothorax. A respiratory rate above 40 breaths per minute, retractions, cyanosis and low oxygen saturation signal impending respiratory failure.

What is the most common cause of shortness of breath?

Cardiopulmonary disease underlies roughly two thirds of presentations. Asthma, COPD, heart failure, pneumonia and coronary artery disease account for nearly 85% of underlying aetiologies; adding interstitial lung disease and psychogenic causes gives the 85% figure reported for patients whose principal symptom is dyspnoea. Where the first-pass workup is normal, the commonest eventual causes were COPD, heart failure, psychogenic causes and deconditioning.

When is shortness of breath considered chronic?

Dyspnoea is considered chronic when it has been present for more than one month. The American Thoracic Society defines dyspnoea itself as a subjective experience of breathing discomfort comprising qualitatively distinct sensations. The one-month threshold matters because it switches the approach from rapid exclusion of emergencies to staged testing across visits.

Can a normal D-dimer rule out pulmonary embolism?

Only when pretest probability is low. A low pretest probability from a validated rule such as Wells, combined with a negative high-sensitivity D-dimer, excludes pulmonary embolism and needs no further workup. With intermediate-to-high pretest probability a D-dimer should not be performed initially, because a negative result cannot safely exclude venous thromboembolism; CT angiography is the test of choice there.

References

• Budhwar N, Syed Z. Chronic Dyspnea: Diagnosis and Evaluation. American Family Physician, 2020;101(9):542-548. aafp.org/pubs/afp/issues/2020/0501/p542.html
• Karnani NG, Reisfield GM, Wilson GR. Evaluation of Chronic Dyspnea. American Family Physician, 2005;71(8):1529-1537. aafp.org/pubs/afp/issues/2005/0415/p1529.html
• Zoorob RJ, Campbell JS. Acute Dyspnea in the Office. American Family Physician, 2003;68(9):1803-1811. aafp.org/pubs/afp/issues/2003/1101/p1803.html
• Wilbur J, Shian B. Diagnosis of Deep Venous Thrombosis and Pulmonary Embolism. American Family Physician, 2012;86(10):913-919. aafp.org/pubs/afp/issues/2012/1115/p913.html
• King M, Kingery J, Casey B. Diagnosis and Evaluation of Heart Failure. American Family Physician, 2012;85(12):1161-1168. aafp.org/pubs/afp/issues/2012/0615/p1161.html
• Cagle SD Jr, Landrum LS, Kennedy AM. Chronic Obstructive Pulmonary Disease: Diagnosis and Management. American Family Physician, 2023;107(6):604-612. aafp.org/pubs/afp/issues/2023/0600/chronic-obstructive-pulmonary-disease.html
• World Health Organization. Chronic obstructive pulmonary disease (COPD) — fact sheet. who.int/news-room/fact-sheets/detail/chronic-obstructive-pulmonary-disease-%28copd%29
• World Health Organization. Asthma — fact sheet. who.int/news-room/fact-sheets/detail/asthma
• World Health Organization. Anaemia — fact sheet. who.int/news-room/fact-sheets/detail/anaemia