Investigations to help diagnose dementia

Some causes of cognitive impairment are reversible and should be excluded before a diagnosis of dementia is made. Assess:

• full blood count—to exclude anaemia and infection
• blood urea, creatinine, electrolyte and calcium concentrations—to exclude various metabolic disturbances and organ failure
• liver biochemistry—if abnormal, see here
• blood glucose concentration to exclude hyperglycaemia or hypoglycaemia
• thyroid function tests—to exclude hypothyroidism or hyperthyroidism
• blood vitamin B12 and folate concentrations—to exclude deficiency.

If the patient is at risk of a sexually transmitted infection, also order syphilis serology and human immunodeficiency virus (HIV) antibody/antigen testing. Symptoms may be due to neurosyphilis or dementia may be associated with HIV.

Unless there is a clear diagnosis of moderate to severe dementia, also request cerebral imaging (eg computed tomography [CT], magnetic resonance imaging [MRI], positron emission tomography [PET]) to exclude other neurological pathologies (eg cerebral space occupying lesions, normal pressure hydrocephalus) and determine dementia subtype.

Although biomarkers (eg cerebrospinal fluid [CSF] beta-amyloid or tau) appear promising, at the time of writing, their role in the diagnosis of dementia remains unclear.