Laboratory Studies
The diagnosis of phencyclidine (PCP) intoxication is a difficult one to make without a history of drug use from the patient. It should be considered in patients with bizarre behavior, hypertension, and nystagmus, or coma unresponsive to naloxone in a substance abuse case.
Exposure to PCP can be confirmed by qualitative urine toxicology screening. Serum screening for PCP is not useful clinically because the test is not readily available. In addition, quantitative serum PCP levels do not correlate with the clin.
A fingerstick glucose test should be performed in all patients with altered mental status, as hypoglycemia can cause symptoms consistent with PCP intoxication. In addition, McCarron et al found that 20% of patients with acute PCP intoxication were hypoglycemic on presentation. [15]
No laboratory tests are specific for PCP intoxication but, in addition to hypoglycemia, elevations in WBC count and BUN and creatinine levels may be seen. Serum creatine phosphokinase and urine myoglobin levels should also be measured to rule out rhabdomyolysis, especially in the patients with severe agitation.
Consider an arterial blood gas (ABG) measurement to assess for hypoxemia and metabolic acidosis in unresponsive patients.
Urine pregnancy tests are indicated for female patients of childbearing age.
Do not rely on the urine toxicology screen to diagnose acute PCP intoxication. Long-term PCP users can have positive test results for weeks after their last use. In addition, false-positive results for PCP have also been reported with many agents, including diphenhydramine (Benadryl) and dextromethorphan, agents in over-the-counter allergy and cough formulations that can produce clinical effects similar to PCP when taken in high doses. [16, 17] Other reported confounders include methadone, ibuprofen, chlorpromazine, and venlafaxine. [18] Consult the laboratory for a list of confounders. If contaminants are a concern, a gas chromatography–mass spectroscopy (GC-MS) confirmatory test can be ordered.
Imaging Studies
No imaging studies are necessary for the evaluation of acute PCP intoxication. Consider a CT scan of the head to rule out an intracranial cause for altered mental status. Consider specific imaging to evaluate traumatic injuries associated with PCP intoxication.
Procedures
For patients who are unable to protect their airway or have evidence of respiratory compromise, endotracheal intubation and mechanical ventilation may be needed.
Consider lumbar puncture in patients with altered mental status and fever in whom the diagnosis is unclear.
