Ordering Recommendation

Use to optimize dosing and monitor patient adherence.

New York DOH Approval Status

This test is New York state approved.

Specimen Required

Patient Preparation

Timing of specimen collection: Predose (trough) draw at steady-state concentration.


Plain red. Also acceptable: Lavender (K2 or K3EDTA) or pink (K2EDTA).

Specimen Preparation

Separate serum or plasma from cells within 2 hours of collection. Transfer 1 mL serum or plasma to an ARUP standard transport tube. (Min: 0.5 mL)

Storage/Transport Temperature


Unacceptable Conditions

Whole blood. Gel separator tubes, light blue (citrate), or yellow (SPS or ACD solution).


After separation from cells: Ambient: 5 days; Refrigerated: 2 weeks; Frozen: 6 months


Quantitative Liquid Chromatography-Tandem Mass Spectrometry


Mon, Wed, Fri


1-7 days

Reference Interval

Effective February 19, 2013

Therapeutic Range Total (doxepin and nordoxepin): 100-300 ng/mL
Toxic Level Greater than 500 ng/mL

Interpretive Data

Toxic concentrations may cause anticholinergic effects and cardiac abnormalities.

Compliance Category

Laboratory Developed Test (LDT)


Hotline History


CPT Codes

80335 (Alt code: G0480)


Component Test Code* Component Chart Name LOINC
0090100 Doxepin, SP 3579-0
0090101 Doxepin/Nordoxepin Total, SP 3582-4
0090105 Nordoxepin, SP 3862-0
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.


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Doxepin and Metabolite, Serum or Plasma (Test on Referral as of 03/05/24)