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Test Code PARO Paroxetine, Serum

Reporting Name

Paroxetine, S

Useful For

Monitoring paroxetine therapy


Identifying noncompliance, although regular blood level monitoring is not indicated in most patients


Identifying states of altered drug metabolism when used in conjunction with CYP2D6 genotyping

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Serum Red

Specimen Required

Container/Tube: Red top

Specimen Volume: 0.5 mL

Collection Instructions: Spin down within 2 hours of draw.

Specimen Minimum Volume

0.4 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Red Refrigerated (preferred) 28 days
  Ambient  28 days
  Frozen  28 days

Reference Values

30-120 ng/mL

Day(s) and Time(s) Performed

Monday, Thursday; 4 p.m.

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
PARO Paroxetine, S 9699-0


Result ID Test Result Name Result LOINC Value
83731 Paroxetine, S 9699-0

Clinical Information

Paroxetine (Paxil and Paxil CR) is approved for treatment of depression. Paroxetine is completely absorbed. Metabolites of paroxetine are inactive. Paroxetine metabolism is carried out by cytochrome P450 (CYP) 2D6. Paroxetine can saturate CYP2D6 resulting in a nonlinear relationship between dose and serum concentration. Paroxetine clearance is significantly affected by reduced hepatic function, but only slightly by reduced renal function.


A typical adult paroxetine dose is 30 mg per day. Paroxetine is 100% bioavailable, 95% protein bound, and the apparent volume of distribution is 17 L/Kg. Time to peak serum concentration is 5 hours for the regular product and 8 hours for the controlled release product. The elimination half-life is 20 hours. Half-life is prolonged in the elderly and with cirrhosis.

Analytic Time

1 day

Reject Due To


Mild OK; Gross OK


Mild OK; Gross OK


Mild OK; Gross OK


Serum gel tube

NY State Approved


Method Name

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