1. Basic metabolic panel, glucose, calcium. Electrolyte abnormalities (hypernatremia, hyponatremia, hypocalcemia) and hypo-glycemia or hyperglycemia can present with alteration of mental status. Metabolic acidosis may point to an underlying metabolic disorder or intoxication. Respiratory acidosis can be seen in intoxications with alcohol, benzodiazepines, and barbiturates.
2. Renal and hepatic profile. Can indicate acute or chronic endorgan dysfunction.
3. CBC with differential. Elevated WBC count may indicate active infection.
4. Toxicology screening and drug levels. Based on patient's history, order blood levels of prescription medications, ingested medications, or substances of abuse.
5. ABGs. Obtain if hypoxia or acid-base problems are suggested by history or physical exam.
6. Lumbar puncture. Perform if history and physical exam suggest an intracranial infection (meningitis or encephalitis); can also demonstrate subarachnoid hemorrhage. Do not perform in the presence of increased intracranial pressure or a space-occupying lesion, because of risk of herniation.
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