Diazepam, Serum or Plasma

CPT: 80346
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Test Details


  • Diastat®
  • Diastat® AcuDial™
  • Diazepam Intensol™
  • Valium®

Test Includes

Diazepam; nordiazepam (diazepam metabolite)


Diazepam is effective in the management of generalized anxiety disorder and panic disorder in appropriately selected patients. Its use prior to endoscopy or cardioversion relieves anxiety and diminishes the patient's recall of the procedure. Preoperative use relieves anxiety and tension and may provide anterograde amnesia. Additional uses include the treatment of skeletal muscle spasms due to inflammation or trauma, spasticity (eg, multiple sclerosis, cerebral palsy, paraplegia, stiff-man syndrome), seizure disorders (eg, status epilepticus, febrile seizures), and alleviation of abstinence symptoms during alcohol withdrawal.


Liquid chromatography/tandem mass spectrometry (LC/MS-MS)

Reference Interval

Therapeutic: diazepam + nordiazepam: 0.2−2.5 μg/mL

Critical Value

Potentially toxic: >5.0 μg/mL

Additional Information

Diazepam is a muscle relaxant and antianxiety drug. Peak blood levels are achieved within an hour after oral dose. Half-life in adults is 21 to 37 hours. The major metabolite (nordiazepam) has a half-life in adults of 50 to 99 hours. It is the major metabolite also of clorazepate and prazepam. Minor active metabolites of diazepam are temazepam (3-hydroxydiazepam) and oxazepam (3-hydroxy-N-diazepam).1,2 Diazepam may exhibit synergism with barbiturates, tricyclic antidepressants, and amine oxidase inhibitors. Toxicity may be additive with other central nervous system depressants, and ethanol enhances the absorption of diazepam itself. Many cases of overdose are seen but few fatalities result from use of this drug alone. A frequent finding is a combination of this drug and ethanol.

Specimen Requirements


Serum or plasma


1 mL

Minimum Volume

0.4 mL


Red-top tube, lavender-top (EDTA) tube, or green-top (heparin) tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.


Transfer separated serum or plasma to a plastic transport tube. Oral: peak: one hour after dose; IV: peak: 15 minutes after dose.

Storage Instructions


Causes for Rejection

Gel-barrier tube

Clinical Information


1. Baselt RC, Cravey RH. Disposition of Toxic Drugs and Chemicals in Man. 4th ed. Foster City, Calif: Chemical Toxicology Institute;1995:222-225.
2. Pellock JM. Safety of Diastat: A rectal gel formulation of diazepam for acute seizure treatment. Drug Saf. 2004; 27(6):383-392. 15144232


American Medical Association, Division of Drugs and Toxicology. Drug Evaluations Subscription. Chicago, Ill: AMA; Summer, 1991.


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
007989 Diazepam (Valium), Serum 019976 Diazepam, Serum ug/mL 3548-5
007989 Diazepam (Valium), Serum 019984 Nordiazepam, Serum ug/mL 3537-8
007989 Diazepam (Valium), Serum 019985 Total (Diaz+Nord) ug/mL 16757-7

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