Acute Confusion

There are hundreds of possible individual causes of confusion. Patients with acute confusion are usually elderly and often present out of hours via a call from an anxious relative or neighbour. The dementias constitute the chronic confusional states, which are not considered here.

Published: 2nd August 2022 | Updated: 6th September 2022

Differential diagnosis

Common Diagnoses

  • Hypoxia (Respiratory and Cardiac)
  • Systemic Infection
  • Cerebrovascular Accident (CVA: Stroke and Transient Ischaemic Attack [TIA])
  • Hypoglycaemia
  • Diabetic Ketoacidosis (DKA)

Occasional Diagnoses

  • Alcohol Withdrawal or Intoxication
  • Cerebral Infection
  • Electrolyte Imbalance and Uraemia
  • Iatrogenic (e.g. Digoxin, Diuretics, Steroids and Opiates)
  • Myxoedema
  • Drug Abuse

Rare Diagnoses

  • Wernicke’s Encephalopathy
  • Cerebral Tumour
  • Hypo- and Hyperparathyroidism
  • Cushing’s Disease
  • Postictal State
  • Carbon Monoxide Poisoning

Ready reckoner

Key distinguishing features of the most common diagnoses

Hypoxia InfectionCVAHypoglycaemiaDKA
Central CyanosisYesPossibleNoNoNo
Focal WeaknessNoNoPossiblePossibleNo

Possible investigations

Likely: Urinalysis, blood sugar (usually glucometer), pulse oximetry.

Possible: FBC, CXR, ECG, cardiac biomarkers, TFT.

Small Print: Calcium, digoxin levels, CT scan.

  • Acute confusion has so many causes and possible presentations that it is difficult to provide a definitive guide of investigations for the GP. A number of investigations might be considered according to the clinical picture and social circumstances; in the majority of cases, the patient will be admitted and necessary tests arranged by the hospital.
  • Urinalysis is very helpful if possible: Look for glucose and ketones (DKA), specific gravity (dehydration), pus, blood and nitrite in UTI. Ketones alone in starvation.
  • A blood glucometer reading is more practical than a formal blood glucose in the acute situation to diagnose hypo- and hyperglycaemia.
  • Pulse oximetry: To detect hypoxia.
  • FBC: Raised WCC in infections. Raised MCV helpful pointer to excess alcohol and myxoedema.
  • U&E important, especially if any signs of dehydration or on diuretics.
  • LFT and TFT: Alcohol, disseminated malignancy and hypothyroidism should always be considered.
  • CXR: May reveal a cause of hypoxaemia (e.g. pneumonia, cardiac failure).
  • ECG, cardiac biomarkers: If silent infarct suspected as cause.
  • Calcium: To detect possible hypo- or hyperparathyroidism.
  • Digoxin levels: For digoxin toxicity.
  • CT scan: Invariably a hospital-based investigation in acute confusion – may reveal spaceoccupying lesion, blood or infarct.

Top Tips

  • The key to management is establishing that the confusion really is acute rather than a gradual deterioration of cognition. This requires a careful history from someone who knows the patient well.
  • Don’t forget a drug history – if little information is available on a visit, check the patient’s medication cupboard.
  • In acute confusional states, it can be difficult to obtain useful clinical pointers from the patient’s history. The examination therefore assumes greater importance than usual.

Red Flags

  • It is virtually impossible to reach a firm diagnosis and treat safely in the home. Be very sure of yourself if you choose not to admit.
  • Central cyanosis is an ominous sign. Give oxygen, if possible, and dial 999.
  • In a diabetic on treatment, always check the blood sugar – remember that hypoglycaemia can produce confusion with neurological signs, mimicking a CVA.
  • Altered physiological responses in the elderly may result in a normal pulse and temperature even in the presence of significant infection. Don’t be misled by this.
  • Ask if any other household members have been unwell – carbon monoxide poisoning could affect others too.
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Website disclaimer

Pulse Reference is based on the best-selling book Symptom Sorter.

The experts behind Pulse Reference are Dr Keith Hopcroft who is the co-author of Symptom Sorter, a GP in Essex and Pulse’s editorial advisor and Dr Poppy Freeman, a GP in Camden and also a clinical advisor to Pulse.

This website is for clinical guidance only and cannot give definitive diagnostic information. Practitioners should work within the limits of their individual professional practice, seek guidance when necessary and refer appropriately.