Overview.
Shortness of breath (dyspnoea) is one of the most alarming symptoms patients experience. While the immediate concern is often lung or heart disease, anaemia is a surprisingly common and easily treatable cause — reduced oxygen-carrying capacity from low haemoglobin makes every activity feel harder. Heart failure biomarkers (BNP/NT-proBNP) can be checked with a simple blood test. Thyroid dysfunction, metabolic acidosis, and obesity all contribute. A targeted lab workup narrows the differential rapidly.
Dyspnoea is the subjective sensation of breathing difficulty — 'air hunger', chest tightness, or feeling unable to take a satisfying breath. It can arise from cardiac, pulmonary, haematological, metabolic, or neuromuscular causes. Acute onset requires urgent evaluation; chronic progressive dyspnoea warrants systematic investigation.
Prevalence: Dyspnoea is the 4th most common reason for GP visits. Affects ~25% of adults in any given month. Causes vary by age: asthma/anxiety in young adults; heart failure/COPD in elderly. Anaemia-related breathlessness is the most commonly overlooked treatable cause.
What to test.
First-line tests
- CBC / Hemoglobin — Anaemia is the most common treatable cause of chronic dyspnoea that blood work can identify. Every 1 g/dL drop in haemoglobin below normal reduces exercise capacity. Iron deficiency anaemia is especially common in women and elderly.
- Ferritin — Iron deficiency causes dyspnoea even before haemoglobin drops (tissue-level iron depletion impairs myoglobin and mitochondrial function). Check alongside CBC.
- CMP — Metabolic acidosis (low bicarbonate) causes compensatory hyperventilation (Kussmaul breathing). eGFR for uraemia. Glucose for diabetic ketoacidosis. Albumin for fluid overload.
- TSH — Hyperthyroidism causes dyspnoea through increased metabolic demand and cardiac output. Hypothyroidism causes dyspnoea through pleural effusion, respiratory muscle weakness, and obesity.
Second-line tests
- BNP or NT-proBNP — The most valuable blood test for heart failure. BNP is released by stretched ventricles. <100 pg/mL (BNP) or <300 pg/mL (NT-proBNP) effectively RULES OUT heart failure. Elevated values identify heart failure even before echocardiography.
- CRP — Elevated with pneumonia, pulmonary embolism, and inflammatory conditions. Helps differentiate infectious from non-infectious causes of acute dyspnoea.
- HbA1c / Fasting Glucose — Undiagnosed diabetes can present with dyspnoea through diabetic ketoacidosis (emergency), heart failure (diabetic cardiomyopathy), or metabolic syndrome-related deconditioning.
Specialized tests
- D-Dimer — Screens for pulmonary embolism (PE) when clinical probability is low-to-moderate. Negative D-dimer effectively rules out PE. Positive D-dimer is NOT diagnostic — requires CT pulmonary angiography for confirmation. Only useful when PE is clinically suspected.
- Troponin — If chest pain accompanies dyspnoea — screens for myocardial injury (heart attack, myocarditis, PE-related right heart strain).
Common causes.
- Anaemia / Iron Deficiency — Gradual onset dyspnoea on exertion, fatigue, dizziness, pallor. Often dismissed as 'deconditioning'.
- Heart Failure — Exertional dyspnoea progressing to orthopnoea (breathless lying flat) and paroxysmal nocturnal dyspnoea (waking at night gasping).
Diagnostic patterns.
- Low hemoglobin + low ferritin + exertional dyspnoea — likely Iron deficiency anaemia. Next step: Iron supplementation; identify source of iron loss (menstruation, GI, malabsorption)
- Elevated BNP (>400 pg/mL) + peripheral oedema + orthopnoea — likely Heart failure. Next step: Echocardiography; cardiology referral; diuretics, ACE/ARB, beta-blocker
- Normal blood work + acute onset + pleuritic chest pain + risk factors — likely Pulmonary embolism. Next step: D-dimer (if low probability) or CT pulmonary angiography (if moderate-high probability)
- Normal blood work + chronic exertional dyspnoea + obesity + deconditioning — likely Deconditioning / obesity-related dyspnoea. Next step: Pulmonary function tests (rule out asthma/COPD); graded exercise programme; weight loss
Lifestyle.
Non-medical causes
- Deconditioning (sedentary lifestyle — most common cause of exertional dyspnoea in younger adults)
- Obesity (restrictive pattern from abdominal weight)
- Anxiety / panic attacks (hyperventilation, air hunger, chest tightness — normal blood work)
- Pregnancy (physiological dyspnoea from progesterone-driven hyperventilation)
- High altitude
- Poor air quality / pollution
Considerations
- Gradual aerobic exercise programme (the most effective treatment for deconditioning-related dyspnoea)
- Weight loss if BMI >30 (reduces respiratory effort and cardiovascular workload)
- Smoking cessation (improves lung function and cardiovascular health)
- Iron-rich diet if ferritin is low (red meat, lentils, spinach + vitamin C for absorption)
- Breathing exercises and diaphragmatic breathing for anxiety-related dyspnoea
- Sleep position: elevate head of bed if orthopnoeic (heart failure symptom)
FAQs.
Can anaemia really make you short of breath?
Absolutely. Haemoglobin carries oxygen to every tissue. When haemoglobin drops, your heart compensates by beating faster and harder — but during exertion, demand exceeds supply. Iron deficiency is particularly insidious because tissue-level iron depletion impairs myoglobin (muscle oxygen storage) even before haemoglobin drops measurably.
What is BNP and should I ask for it?
BNP (B-type natriuretic peptide) is released by heart muscle when it's stretched by fluid overload. A normal BNP (<100 pg/mL) effectively rules out heart failure as a cause of dyspnoea — it's that useful. If you have unexplained breathlessness with ankle swelling or orthopnoea, BNP is the most informative single blood test.
My breathing is fine at rest but I get winded walking upstairs — is that normal?
It depends on your fitness level, age, and how long it takes to recover. If it's new, progressive, or disproportionate to your activity level, check: CBC (anaemia), ferritin (iron), TSH (thyroid). For most healthy adults, getting slightly winded climbing 3+ flights is normal. Unable to climb 1 flight without stopping warrants investigation.