~3%
lifetime prevalence of psychotic disorders
2–3yr
average delay to first diagnosis
No
single definitive biomarker test
Diagnosing psychosis is a clinical process — there is no single blood test or brain scan that confirms it. Clinicians integrate a structured psychiatric interview, validated rating scales, medical investigations, and the patient's history to reach a diagnosis using DSM-5-TR or ICD-11. The goal is to confirm psychotic symptoms and rule out organic or substance-induced causes.
01 · Diagnostic Pathway
The Five-Stage Diagnostic Process
1
Referral & Presentation
Patient referred by GP, ER, or self-referral; onset and history documented
2
Psychiatric Interview
Structured clinical interview; comprehensive mental state examination
3
Symptom Rating
Standardised scales quantify severity and type of psychotic symptoms
4
Medical Rule-Out
Labs, imaging, and neurological tests exclude organic causes
5
Formulation & Diagnosis
DSM-5-TR / ICD-11 criteria applied; diagnosis and care plan established
02 · Diagnostic Criteria
DSM-5-TR Core Criteria
For Schizophrenia (most common psychotic disorder)
Delusions
Fixed false beliefs resistant to contrary evidence
Hallucinations
Perceptions without external stimulus; auditory most common
Disorganised Speech
Incoherence, derailment, or loose associations
Disorganised Behaviour
Grossly disturbed or catatonic behaviour
Negative Symptoms
Diminished emotional expression, avolition, alogia, anhedonia, asociality
Criterion A: ≥2 symptoms for ≥1 month; at least one must be delusions, hallucinations, or disorganised speech. Total duration ≥6 months.
ICD-11 Framework
World Health Organization classification
Primary Psychotic Disorders
Schizophrenia, schizoaffective disorder, delusional disorder, acute & transient psychotic disorder, schizotypal disorder
Six Symptom Dimensions
Positive, negative, depressive, manic, psychomotor, and cognitive symptom specifiers
Duration Thresholds
Schizophrenia: ≥1 month. Acute & transient psychosis: onset within 2 weeks; full remission possible
Functional Impact Required
Significant decline in occupational, social, or self-care functioning required for diagnosis
Rule-Out: What Must Be Excluded First
Differential Diagnosis Essentials
Substance-InducedStimulants, cannabis, hallucinogens, alcohol withdrawal — can mimic full psychosis
Medical ConditionsEpilepsy, autoimmune encephalitis, brain tumour, thyroid disorders, B12 deficiency
Mood DisordersBipolar I with psychotic features; severe depression with psychosis must be distinguished
DeliriumAcute confusional state with fluctuating consciousness — usually has an organic cause
03 · Clinical Interview Tools
Structured Diagnostic Interviews
Formal interview instruments
SCID-5
Structured Clinical Interview for DSM-5
Gold-standard semi-structured interview mapping to DSM-5 criteria; covers psychosis, mood, anxiety, and substance use
MINI
Mini International Neuropsychiatric Interview
Brief structured interview (~20 min); widely used for rapid diagnostic screening in research and clinical settings
CAINS
Clinical Assessment Interview for Negative Symptoms
Specifically targets negative symptoms with detailed probing of motivation, pleasure, and social functioning
CAARMS
Comprehensive Assessment of At-Risk Mental States
Identifies individuals in prodromal / ultra-high-risk stages before full psychosis onset develops
Mental State Examination (MSE)
Core domains assessed in every evaluation
Appearance
Dress, hygiene, eye contact, psychomotor activity, and posture
Speech
Rate, rhythm, volume, coherence, thought form (loosening, flight of ideas)
Mood & Affect
Subjective mood vs. observed affect; flat or incongruent affect common in psychosis
Thought Content
Delusions, overvalued ideas, obsessions, suicidal or homicidal ideation
Perception
Hallucinations (auditory, visual, olfactory, tactile), illusions, depersonalisation
Cognition & Insight
Orientation, memory, concentration; level of insight into illness and treatment
04 · Validated Rating Scales
Psychosis Symptom Severity Scales
Quantify symptoms, track treatment response, and guide clinical decisions
PANSS
Positive & Negative Syndrome Scale
30-item scale: positive (7), negative (7), general psychopathology (16). Most widely used in research and clinical trials.
BPRS
Brief Psychiatric Rating Scale
18–24 item multi-domain assessment. Widely used in emergency and inpatient psychiatric settings for rapid evaluation.
SAPS / SANS
Scale for Assessment of Positive/Negative Symptoms
SAPS: hallucinations, delusions, thought disorder. SANS: negative symptoms in depth (Andreasen).
PSYRATS
Psychotic Symptom Rating Scales
Rates hallucinations and delusions on frequency, distress, duration, and perceived control.
CGI-SCH
Clinical Global Impression – Schizophrenia
Global severity and change over time; quick format for routine outpatient care.
CAPE / PROD
Community Assessment / PROD Screen
Self-report early-detection tools flagging at-risk individuals for specialist referral.
05 · Medical & Laboratory Investigations
Blood Tests
Exclude organic causes
Full Blood Count (FBC)
Anaemia, infection, or haematological conditions causing psychiatric symptoms
Metabolic Panel
Glucose, electrolytes, renal and liver function — screens for metabolic encephalopathy
Thyroid Function Tests
Hypo/hyperthyroidism can both cause pronounced psychotic features
Autoimmune Screen
NMDA-R antibodies, ANA — screens for autoimmune encephalitis (anti-NMDAR)
Toxicology / Drug Screen
Urine or serum screen essential to rule out substance-induced psychosis
Vitamins B12 & Folate
Deficiency can manifest with neuropsychiatric and psychotic symptoms
Neuroimaging & EEG
Structural & functional brain investigation
MRI Brain
Rule out tumour, demyelination, stroke, encephalitis, temporal lobe pathology
CT Head
Rapid first-line scan; detects gross lesions and haemorrhage
EEG
Epilepsy-related psychosis; ictal or postictal psychiatric states
fMRI / PET
Research: maps dopaminergic dysfunction and connectivity changes
Note: Neuroimaging is indicated in first-episode psychosis, atypical presentations, focal neurological signs, or sudden onset.
Cognitive & Psych Testing
Neuropsychological assessment battery
MCCB
MATRICS Consensus Cognitive Battery — 7 domains; standard for measuring cognitive deficits in schizophrenia
MMSE / MoCA
Brief bedside screens; detect dementia or delirium overlapping with psychotic presentation
WAIS-IV
Full IQ assessment; reveals premorbid functioning decline in early psychotic disorders
Personality Assessment
MMPI-2, Rorschach — differential from personality disorders and dissociative presentations
Social Cognition Scales
Theory of mind, emotion recognition — deficits unique to the psychotic spectrum
Special Diagnostic Considerations
Context-specific factors shaping the diagnostic process
First Episode
Extensive workup required; organic causes are more frequent and more often missed at first presentation
Children & Adolescents
Very-early-onset schizophrenia requires careful developmental assessment (K-SADS, ADOS for ASD differential)
Older Adults
Late-onset psychosis warrants dementia workup; hearing and vision impairment can contribute or mimic psychosis
Cultural Context
Cultural beliefs and language barriers must be considered; culturally adapted instruments and interpreters preferred