Schizophrenia is a complex mental health disorder characterized by symptoms like hallucinations, delusions, disorganized thinking, and negative symptoms (e.g., lack of motivation). There is no single lab test or scan to diagnose it definitively. Instead, doctors use a comprehensive, multi-step evaluation based on criteria from the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) or International Classification of Diseases (ICD-11).

The process begins with a detailed psychiatric interview. A psychiatrist or trained clinician asks about symptoms, their onset, duration (must persist for at least 6 months, with active symptoms for 1 month), and impact on daily life. They explore family history, as genetics play a role first-degree relatives increase risk 10-fold. Medical, substance use, and social histories rule out mimics like drug-induced psychosis or bipolar disorder.

Physical and neurological exams follow to exclude organic causes. Blood tests screen for infections, thyroid issues, vitamin deficiencies (e.g., B12), or toxins. Urine toxicology detects substances like amphetamines or cannabis that can trigger similar symptoms.

Brain imaging, such as MRI or CT scans, identifies structural abnormalities (e.g., enlarged ventricles) or rules out tumors, strokes, or autoimmune encephalitis (via anti-NMDA receptor antibodies). EEG may detect seizures mimicking psychosis.

Psychological assessments include standardized tools like the Positive and Negative Syndrome Scale (PANSS) or Brief Psychiatric Rating Scale (BPRS) to quantify symptoms. Cognitive tests evaluate attention, memory, and executive function, often impaired in schizophrenia.

Diagnosis requires at least two core symptoms (delusions, hallucinations, disorganized speech/thought, grossly disorganized behavior, or negative symptoms) for a significant portion of one month, plus functional decline. Differential diagnosis excludes schizoaffective disorder, PTSD, or neurodevelopmental conditions like autism.

Early diagnosis improves outcomes with antipsychotics and therapy. If symptoms emerge, seek a specialist promptly—self-diagnosis is unreliable.