Tricyclic Antidepressant Screen

The tricyclic antidepressant (TCA) screen is a laboratory test used to detect the presence of tricyclic antidepressants in a patient's blood or urine.

Purpose

The purpose of the TCA screen is to:

• Detect and monitor TCA levels in patients taking these medications for therapeutic purposes
• Identify potential overdose or toxicity cases
• Aid in the diagnosis of adverse reactions or side effects related to TCA use

Procedure

The TCA screen typically involves:

• Blood collection: A blood sample is drawn from a vein, usually in the arm
• Urine collection: A urine sample may be collected instead of or in addition to a blood sample
• Laboratory analysis: The collected sample is sent to a laboratory for analysis using techniques such as gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-tandem mass spectrometry (LC-MS/MS)

Interpretation of Results

The results of the TCA screen are typically reported as:

• Qualitative results: The presence or absence of TCAs in the sample
• Quantitative results: The concentration of TCAs in the sample, usually measured in nanograms per milliliter (ng/mL) or micrograms per liter (μg/L)

Reference Ranges

The reference ranges for TCA levels vary depending on the laboratory and the specific medication being tested. Generally:

• Therapeutic levels: 50-300 ng/mL for most TCAs
• Toxic levels: >1000 ng/mL for most TCAs

Clinical Significance

The TCA screen is clinically significant because:

• TCAs can have serious side effects, such as cardiac arrhythmias and seizures, at high concentrations
• Overdose or toxicity cases require prompt medical attention
• Monitoring TCA levels can help optimize therapeutic dosing and minimize adverse reactions

Limitations

The TCA screen has some limitations, including:

• Cross-reactivity with other medications or substances may occur
• False-negative results may be obtained if the sample is collected too soon after ingestion or if the patient has taken a medication that interferes with the test
• False-positive results may be obtained if the sample is contaminated or if there is interference from other medications or substances