Anaphylaxis DDx


Anaphylaxis is a severe, life-threatening, generalised or systemic hypersensitivity reaction. It is characterised by rapidly developing life-threatening airway (pharyngeal or laryngeal edema) and/or breathing (bronchospasm and tachypnea) and/or circulation (hypotension and tachycardia) problems usually associated with skin and mucosal changes.

Causes of Anaphylaxis


  • Insect stings (most commonly honeybee, ants, wasps)
  • Foods (most commonly peanuts, tree nuts, and seafood in adults; eggs, cows milk, dairy products, seeds, and fruit in children)
  • Medications (most commonly antibiotics, non-steroidal anti-inflammatory drugs, contrast-induced anaphylactoid reactions, immunotherapy)
  • Unidentified (no cause found, more than 50% of cases)


  • Physical triggers (exercise, heat, cold, UV light)
  • Biological fluids (transfusions, immunoglobulin, antivenoms, semen)
  • Latex
  • Tick bites
  • Hormonal changes (breastfeeding, menstrual factors)
  • Dialysis membranes (haemodialysis-associated anaphylaxis)
  • Hydatid cyst rupture
  • Aeroallergens (domestic/laboratory animals, pollen)
  • Food additives (monosodium glutamate, metabisulfite, preservatives, colours, natural food chemicals)
  • Topical medications (antiseptics)

Differential diagnosis of conditions that mimic anaphylaxis

  • Tissue swelling
    • Idiopathic urticaria
    • Isolated angioedema
      • Idiopathic
      • Angiotensin-converting enzyme inhibitor-induced
      • Acquired or hereditary C1 esterase inhibitor deficiency
  • Conditions mimicking upper airway oedema
    • Dystonic reactions mimicking symptoms of a swollen tongue
    • Acute oesophageal reflux (sudden onset of painful throat “swelling”)
  • Flushing syndromes
    • Peptide-secreting tumours (eg, carcinoid syndrome, VIPomas)
    • Alcohol-related
    • Medullary carcinoma of thyroid
    • Red man syndrome (associated with vancomycin infusion)
  • Neurological syndromes
    • Epileptic seizure
    • Stroke
  • Other causes of collapse
    • Vasovagal episodes
    • Systemic inflammatory response syndrome
    • Shock due to other causes
  • Acute respiratory distress
    • Asthma
    • Panic disorders
    • Globus hystericus
    • Laryngospasm
    • Vocal cord dysfunction
  • Miscellaneous
    • Scombroid fish poisoning
    • Serum sickness
    • Phaeochromocytoma
    • Systemic mastocytosis

CCC Differential Diagnosis Series


Anosmia, Ataxia, Blepharospasm, Bulbar and Pseudobulbar palsy, Central Pontine Myelinosis, Cerebellar Disease, Chorea, Cranial nerve lesions, Dementia, Dystonia, Exophthalmos, Eye trauma, Facial twitches, Fixed dilated pupil, Horner syndrome, Loss of vision, Meningism, Movement disorders, Optic disc abnormality, Parkinsonism, Peripheral neuropathy, Radiculopathy, Red eye, Retinal Haemorrhage, Seizures, Sudden severe headache, Tremor, Tunnel vision


Bronchial breath sounds, Bronchiectasis, High airway pressures, Massive haemoptysis, Sore throat, Tracheal displacement


Atrial Fibrillation, Bradycardia, Cardiac Failure, Chest Pain, Murmurs, Post-resuscitation syndrome, Pulseless Electrical Activity (PEA), Pulsus Paradoxus, Shock, Supraventricular tachycardia (SVT), Tachycardia, VT and VF, SVC Obstruction


Abdominal distension, Abdominal mass, Abdominal pain, Asterixis, Dysphagia, Hepatomegaly, Hepatosplenomegaly, Large bowel obstruction, Liver palpation abnormalities, Lower GI haemorrhage, Malabsorption, Medical causes of abdominal pain, Rectal mass, Small bowel obstruction, Upper GI Haemorrhage


Genital ulcers, Groin lump, Scrotal mass, Urine colour, Urine Odour, Urine transparency


Arthritis, Shoulder pain, Wasting of the small muscles of the hand


Palmar erythema, Serious skin signs in sick patients, Thickened Tethered Skin, Leg ulcers, Skin Tumour, Acanthosis Nigricans


Diabetes Insipidus, Diffuse Goitre, Gynaecomastia, Hirsutism, Hypoglycaemia, SIADH, Weight Loss




Floppy infant 


Anaphylaxis, Autoimmune associated diseases, Clubbing, Parotid Swelling, Splinter haemorrhages, Toxic agents and abnormal vitals, Toxicological causes of cardiac arrest


CHEST: Atelectasis, Hilar adenopathy, Hilar enlargement on CXR, Honeycomb lung, Increased interstitial markings, Mediastinal widening on mobile CXR, Pulmonary fibrosis, Pseudoinfiltrates on CXR, Pulmonary opacities on CXR,
Gas on abdominal X-ray, Kidney mass,
Intracranial calcification, Intracranial structures with contrastVentriculomegaly,
OTHER: Pseudofracture on X-Ray


LOW: Anaemia, Hypocalcaemia, hypochloraemia, Hypomagnesaemia

HIGH: Bilirubin and Jaundice, HyperammonaemiaHypercalcaemia, Hyperchloraemia, Hyperkalaemia, Hypermagnesaemia

ACID BASE: Acid base disorders, Resp. acidosis, Resp. alkalosis,

Creatinine, CRP, Dipstick Urinalysis, Laboratory Urinalysis, Liver function tests (LFTs), Pleural fluid analysis, Urea, Urea Creatinine Ratio, Uric acid, Urinalysis, Urine Electrolytes


CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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