Lab Test

Doxepin Level (including Nordoxepin)

Sinequan, Doxepin Level

Test Codes

Antrim #17252, EPIC: LAB1230982, SOFT: DOXEP



Specimen Collection Criteria

Collect: One plain Red-top tube. (Minimum Whole Blood: 2.0 mL)

Do not use Serum Separator Tubes.
Time of Collection:
Trough, just prior to the next dose.
Record the exact time of specimen collection on the tube or in the computer system.

Physician Office/Draw Specimen Preparation

Let specimens clot 30-60 minutes. Centrifuge specimen to separate serum from cells. Refrigerate (2-8°C or 36-46°F) the centrifuged collection tube within two hours of collection. (Minimum: 0.5 mL serum)

Preparation for Courier Transport

Transport: Centrifuged collection tube, refrigerated (2-8°C or 36-46°F). (Minimum: 0.5 mL serum)

Rejection Criteria

  • Serum Separator (SST) tubes.
  • Severely lipemic or hemolyzed specimens. 

In-Lab Processing

Let specimens clot 30-60 minutes. Centrifuge specimen to separate serum from cells. Deliver immediately to the appropriate testing station.


Specimen Stability for Testing:

Room Temperature (20-26°C or 68-78.8°F): 24 hours
Refrigerated (2-8°C or 36-46°F): 7 days
Frozen (-20°C/-4°F or below): 3 months

Specimen Storage in Department Prior to Disposal:

Frozen (-20°C/-4°F or below): 2 months


Royal Oak Toxicology Laboratory


Monday, Thursday.
Results available the same day as testing performed (1-4 days).

Reference Range

Doxepin + Nordoxepin: 75-200 ng/mL.
Critical: Greater than 500 ng/mL total.

Test Methodology

Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS).

This test was developed and its performance characteristics determined by Beaumont Health. It has not been cleared or approved by the FDA. The Laboratory is regulated under CLIA as qualified to perform high-complexity testing. This test is used for clinical purposes and should not be regarded as investigational or for research.


Tricyclic antidepressants can display cardiotoxicity in the elderly and susceptible adults and children.

Clinical Utility

This assay is used to monitor the therapeutic drug level and evaluate the toxicity of doxepin. Doxepin is a tricyclic antidepressant used to treat depression. Nordoxepin is the major active metabolite of doxepin.

CPT Codes

80337 (alternate: G0480).
LOINC:  3582-4, Doxepin 3579-0, 61415-6, Nordoxepin 3862-0, 58014-2, Doxepin Plus Nordoxepin 3582-4


Last Updated


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