What lab tests should a patient on antidepressants, such as (sertraline) (Selective Serotonin Reuptake Inhibitor), have for a basic check?

Laboratory Monitoring for Patients on Sertraline (SSRIs)

For routine monitoring of patients on sertraline or other SSRIs, no specific laboratory tests are required for basic checks. 1, 2

Baseline and Routine Laboratory Testing

The FDA label for sertraline does not mandate any routine laboratory monitoring for patients on stable antidepressant therapy. 2 The primary laboratory considerations are:

When Laboratory Tests ARE Indicated:

Prothrombin Time/INR Monitoring:

• Monitor prothrombin time carefully when initiating or discontinuing sertraline in patients taking warfarin, as sertraline causes a mean 8% increase in prothrombin time. 2
• This monitoring should occur at treatment initiation and discontinuation, not routinely during stable therapy. 2

Lithium Levels (if applicable):

• Monitor plasma lithium levels following initiation of sertraline therapy in patients on concurrent lithium, though sertraline does not significantly alter steady-state lithium levels or renal clearance. 2
• Adjust lithium dosing as needed based on levels. 2

When Laboratory Tests Are NOT Routinely Recommended:

Therapeutic Drug Monitoring (TDM):

• Routine measurement of sertraline plasma concentrations is not recommended, as correlations between plasma levels and therapeutic effects are sparse. 1, 3
• The therapeutic range of 10-50 ng/mL exists but has limited clinical utility for routine monitoring. 1
• TDM may be considered only in specific situations: suspected non-compliance, lack of clinical response at recommended doses, suspected drug interactions, or unusual adverse effects. 4

Pharmacogenetic Testing:

• CYP2C19 genotyping is not routinely recommended before starting sertraline, though it may be classified as "potentially beneficial" in treatment-resistant cases. 1, 5
• The EGAPP Working Group found insufficient evidence to recommend routine CYP450 genetic testing for patients starting SSRI treatment. 4, 1
• CYP2C19 ultra-metabolizers have higher prevalence among SSRI non-responders, but testing should be reserved for patients with treatment failure rather than as baseline screening. 1, 5

Important Clinical Monitoring Caveats:

False-Positive Drug Screens:

• Be aware that sertraline causes false-positive urine immunoassay screening tests for benzodiazepines due to lack of specificity. 2
• False-positive results may persist for several days after discontinuation. 2
• Confirmatory testing with gas chromatography/mass spectrometry will distinguish sertraline from benzodiazepines. 2

No Routine Metabolic Monitoring:

• Unlike some other psychotropic medications, sertraline does not require routine monitoring of liver function tests, renal function, electrolytes, or complete blood counts in otherwise healthy patients. 3, 6, 7

Bottom Line Algorithm:

1. Baseline: No routine labs required before starting sertraline
2. During stable therapy: No routine labs required
3. Special circumstances only:
   • PT/INR if on warfarin (at initiation/discontinuation)
   • Lithium levels if on lithium (at initiation)
   • Consider CYP2C19 testing only after treatment failure
   • TDM only for suspected non-compliance or unexplained lack of response