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UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: Ethosuximide

Test Code(s): ESUX / XETHO

CPT Code(s): 80168

Methodology: Gas Chromatography

Clinical Significance: Anticonvulsant

Days Performed: Daily, dayshift.

Turnaround Time: Routine: 24 hours.

Specimen Requirements

Specimen: Blood

Collection Instructions: Collect specimen for trough level prior to next dose.

Collection Container: Preferred: Red top

Collection Volume: Preferred: 3 mL
Pediatrics: 1 mL

Sample Analyzed: Serum

Volume Required: Preferred: 1 mL
Pediatrics: 0.4 mL

Specimen Processing: Centrifuge. Transfer cell-free serum to plastic vial. Refrigerate.

Specimen Transport: Transport specimen to UWHC Core Laboratory (B4/220). Transport with coolant pack if coming from outreach location.

Unacceptable Criteria: Specimens collected in red cap with yellow ring (SST) tubes are not acceptable.

Stability: Ambient: 12 hours
Refrigerated: 2 days
Frozen: 1 year


Interpretive Guidelines:
Generally effective therapeutic concentration:  
18 years and up:   40.0-100.0 mcg/mL


Critical Calls: View

Additional Information:

Result of "BELOW" indicates that the result is below the method detection limit of 1 mcg/mL. The half-life is 40-60 hours in adults, 30-50 hours in children. Ethosuximide has been reported to cause elevation of serum phenytoin concentrations when two drugs are given concurrently. Concurrent therapy with valproic acid has been reported to cause elevations in ethosuximide concentrations.


This test was developed and its performance characteristics determined by the UWHC Clinical Laboratories.  This test meets the standards for clinical testing.  This test should not be regarded as investigational or for research use.  The US Food and Drug Administration (FDA) has not approved or cleared this test; however, the FDA has determined that such clearance or approval is not necessary.


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