CPT: 80342
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Test Details


  • Thorazine®


Evaluate toxicity; monitor therapeutic levels


This test was developed and its performance characteristics determined by LabCorp. It has not been cleared or approved by the Food and Drug Administration.


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

Reference Interval

Therapeutic: 30−300 ng/mL

Critical Value

Potentially toxic: >750 ng/mL

Additional Information

The drug is used in the management of psychotic disorders, control of nausea, preventing apprehension before surgery, acute porphyria, treatment of tetanus, and intractable hiccups. Although intestinal absorption is complete, the oral bioavailability is 32%±19% because of variable metabolism in the intestinal wall and liver (marked first-pass effect). Time to peak plasma concentration is two to four hours. After intramuscular administration, peak plasma concentrations are 4 to 10 times higher than after oral administration; onset of action occurs within 20 to 30 minutes, and the peak levels are noted in two to three hours. Volume of distribution (21±9 L/kg) is high and plasma binding (95% to 98%) is extensive. Clearance after intramuscular administration is 8.6±2.9 mL/minute/kg. Less than 1% of the drug is excreted unchanged by the kidney. The nominal elimination plasma half-life is 30±7 hours; however, some metabolites are eliminated slowly (months) in the urine. Hepatic enzyme induction with increased clearance usually is a minor effect that varies considerably among individuals.

At least 100 metabolites of chlorpromazine appear in humans; most are minor. Several, including 7-hydroxychlorpromazine, 11-hydroxychlorpromazine, norchlorpromazine, and possibly chlorpromazine N-oxide, are neuropharmacologically active.

Specimen Requirements


Serum or plasma


1 mL

Minimum Volume

0.5 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.

Storage Instructions

Room temperature

Stability Requirements



Room temperature

14 days


14 days


14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Gel-barrier tube

Clinical Information


American Medical Association. Division of Drugs and Toxicology. Drug Evaluations Subscription. Chicago, Ill: AMA, Winter 1992.
Drug Information Handbook. 24th ed. Hudson, OH: Wolters Kluwer Clinical Drug Information, Inc; 2015; 429.


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
072132 Chlorpromazine, Serum 3471-0 072132 Chlorpromazine, Serum ng/mL 3471-0

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