Synopsis
Use history-led physical examination and proportionate baseline tests to identify acute medical or neurological causes, establish safe treatment parameters and avoid both diagnostic overshadowing and indiscriminate investigation in psychiatric presentations.
- Start with vital signs, oxygen saturation, consciousness and bedside glucose when illness, intoxication, withdrawal or altered behaviour could reflect physiological disturbance.
- Perform a complete examination when presentation is acute or unexplained, adding focused neurological, cardiovascular, endocrine, injury, infection and nutritional assessment from the history.
- Select tests to answer stated questions; there is no universal blood panel that proves a presentation is medically cleared for psychiatric care.
- Common initial tests may include FBC, renal and liver profiles, electrolytes, calcium, glucose, thyroid function and pregnancy testing when clinically relevant and consented.
- Use ECG before or during medicines with cardiac or QT implications and when syncope, chest symptoms, electrolyte disturbance, overdose or stimulant exposure is possible.
- Toxicology results are limited by detection windows, cross-reactivity and incomplete panels; a negative screen does not exclude substance involvement and a positive result does not prove causation.
- Brain imaging, lumbar puncture, EEG, infection testing and autoimmune work-up are targeted by onset, course, examination and risk rather than ordered routinely.
- Record baseline weight, waist or BMI, pulse, blood pressure and relevant metabolic markers before antipsychotic treatment where urgency permits, without delaying necessary emergency care.
- Explain tests, seek consent, preserve dignity and assign responsibility for results and follow-up, including abnormalities discovered after transfer or discharge.
Key red flags
First psychiatric symptoms after age 40, abrupt onset, rapid progression or prominent cognitive change should lower the threshold for medical and neurological investigation.
Fever, autonomic instability, rigidity, clonus, reduced consciousness or recent psychotropic change can signal serotonin toxicity, neuroleptic malignant syndrome, withdrawal or encephalitis.
New seizure, focal signs, severe headache, head trauma, papilloedema, abnormal movements or catatonia warrants urgent neurological assessment and targeted imaging or electroencephalography.
Pregnancy, postpartum state, immunosuppression, endocrine symptoms, malnutrition or substantial substance exposure changes both differential diagnosis and test selection.
A normal screening panel cannot rule out conditions such as epilepsy, autoimmune encephalitis, early infection or intermittent intoxication when the phenotype remains concerning.
Investigation priorities
Identify hypoxia, fever, hypotension, tachycardia, hypoglycaemia and altered consciousness requiring emergency treatment.
Management branches
Behavioural or mental-state change is sudden, severe, fluctuating or accompanied by physical warning features.
- Use ABCDE, observations, glucose and focused history for medicines, substances, trauma, seizure, infection and baseline cognition.
- Perform targeted physical and neurological examination and request time-critical tests based on the suspected syndrome.
- Treat abnormalities and arrange the correct medical setting, maintaining psychiatric risk precautions and a clear cross-specialty handover.