Sign in →

Test Code LAB31 Phenytoin, Total, Blood

Performing Laboratory

St. Louis Children's Hospital - Chemistry

Specimen Requirements

Patient Preparation: None

Container/Tube  
Preferred: Mint green-top Lithium Heparin (MNTGRN LiHep) tube
Acceptable: Green samplette/microtainer, plain red-top tube, Gold SST gel tube, or Lavender-top (EDTA) tube.

Collection Volume: 1.0 mL (minimum 0.6 mL)

Submission Container/Tube: If specimen is coming from outside facility and collected in a microtainer or plain red-top tube aliquot processed sample into a plastic vial for transport (labeling with specimen type).
Special Instructions: Send to lab promptly. 

NOTE: If patient is receiving fosphenytoin, collect at least 2 hours after an intravenous dose and at least 4 hours after intramuscular dose

Sample Rejection

Mislabeled or unlabeled specimens

Logistics

Test Availability: Monday-Sunday
Cut-off time: None; performed as received
Turnaround Time: Same day; 2 hours from receipt in lab

Reference Values

Therapeutic Range: 

all ages: 10.0-20.0 mcg/mL                                                                      

Critical Values: >60.0 mcg/mL

Critical test results will be automatically called back initially and every 24 hours thereafter.

Methodology

Kinetic interaction of microparticles in solution (KIMS)

Limitations

  • As with any assay employing mouse antibodies, the possibility exists for interference by HAMA in the sample, which could cause falsely low results.

For diagnostics purposes, the results should always be assessed in conjunction with the patient's medical history, clinical examination, and other findings.

Additional Information

FOR SLCH CORE LABORATORY USE ONLY

Lab Processing Instructions: Centrifuge specimen to separate. If specimen is collected in a plain red-top tube, microtainer, or Lavender-top (EDTA) tube aliquot sample into a Roche false-bottom tube for testing (labeling with specimen type).
Processed Volume: 0.3 mL plasma/serum
Analyte Stability:

Specimen Type Temperature Time  
Whole Blood (unprocessed)  Ambient NA  
Plasma/Serum (processed) Refrigerated (preferred) 4 days  
  Ambient  2 days  
  Frozen  1 month       

LOINC

3968-5

Last Reviewed

06/2025

Test Classification and CPT Coding

80185