medical illnesses. Excluding medical illnesses associated with psychosis is performed by using blood tests to measure: Thyroid-stimulating hormone to exclude hypo- or hyperthyroidism, Basic electrolytes and serum calcium to rule out a metabolic disturbance, Full blood count including ESR to rule out a systemic infection or chronic disease, and Serology to exclude syphilis or HIV infection. Other investigations include: EEG to exclude epilepsy, and an MRI or CT scan of the head to exclude brain lesions. Because psychosis may be precipitated or exacerbated by common classes of medications, medication-induced psychosis should be ruled out, particularly for first-episode psychosis. Both substance- and medication-induced psychosis can be excluded to a high level of certainty, using toxicology screening. Because some dietary supplements may also induce psychosis or mania, but cannot be ruled out with laboratory tests, a psychotic individual's family, partner, or friends should be asked whether the patient is currently taking any dietary supplements. Common mistakes made when diagnosing people who are psychotic include: Not properly excluding delirium, Not appreciating medical abnormalities (e.g., vital signs), Not obtaining a medical history and family history, Indiscriminate screening without an organizing framework, Missing a toxic psychosis by not screening for substances and medications, Not asking their family or others about dietary supplements, Premature diagnostic closure, and Not revisiting or questioning the initial diagnostic impression of primary psychiatric disorder. Only after relevant and known causes of psychosis are excluded, a mental health clinician may make a psychiatric differential diagnosis using a person's family history, incorporating information from the person with psychosis, and information from family, friends, or significant others. Types of psychosis in psychiatric disorders may be established by formal rating scales. The Brief Psychiatric Rating Scale (BPRS) assesses the level of 18 symptom constructs of psychosis such as hostility, suspicion, hallucination, and grandiosity. It is based on the clinician's interview with the patient and observations of the patient's behavior over the previous 2–3 days. The patient's family can also answer questions on the behavior report. During the initial assessment and the follow-up, both positive and negative symptoms of psychosis can be assessed using the 30 item Positive and Negative Symptom Scale (PANSS). The DSM-5 characterizes disorders as psychotic or on the schizophrenia spectrum if they involve hallucinations, delusions, disorganized thinking, grossly disorganized motor behavior, or negative symptoms. The DSM-5 does not include psychosis as a definition in the glossary, although it defines "psychotic features", as