Investigations should be directed towards potential risk factors for, or causes of, the delirium found from the history and examination.

Routine investigations

The following should be routine in any confused patient:

At the bedside:

  • Oxygen saturation
  • Blood glucose (finger prick)
  • Electrocardiogram
  • Urine dipstick +/- MSU
  • Chest x-ray

In the laboratory:

  • Full blood count
  • U&E
  • Glucose

Specific laboratory tests

Other specific laboratory tests to consider, depending on initial assessment findings, are:

  • Arterial blood gases +/-carboxyhaemoglobin
  • LFT
  • Coag
  • TFT
  • Blood cultures
  • Drug levels (e.g. theophylline, digoxin)
  • B12, folate, VDRL, autoimmune screen
  • D-Dimer (only as part of focussed DVT/pulmonary embolism work up)

Computerised Tomography (CT) scanning

There is no evidence for the use of routine CT head scanning in the initial investigation of acute delirium. Indications for CT in the investigation of acute delirium are:

  • Focal neurologial signs
  • Confusion after a head injury or fall
  • Evidence of raised intracranial pressure

Lumbar puncture (LP)

LP should be reserved for patients in whom meningitis, or another central nervous system (CNS) infective cause, is suspected.

There is no evidence for its routine use.