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22772 Phenytoin

Phenytoin
Test Code: PTN
Synonyms/Keywords
Dilantin, DPH, Diphenylhydantoin​
Useful For
Phenytoin (5,5-diphenylhydantoin) is one of the most widely prescribed drugs for the treatment of seizure disorders. It is considered one of the drugs of choice for generalized major motor (grand mal epilepsy) and focal seizures. ​
Specimen Requirements
Fasting Required Specimen Type Preferred Container/Tube Acceptable Container/Tube Specimen Volume Specimen Minimum Volume
(allows for 1 repeat)		 Pediatric Minimum Volume
(no repeat)
No​ Serum​ Serum Separator Tube (SST) ​Red Top Tube (RTT)​ 0.5 mL​ 0.2 mL​ 0.4 mL whole blood​
Collection Processing Instructions
Indicate time of collection.
Separate serum from cells within 1 hour of collection if using RTT.
Serum must be removed from gel within 24 hours of collection.
Specimen Stability Information
Specimen Type Temperature Time
Serum​ ​ ​ Room Temperature 8 hours
Refrigerate​ 7 days​
Frozen​ 30 days
Performing Laboratory Information
Performing Location Day(s) Test Performed Analytical Time Methodology/Instrumentation
Weston​​ ​Monday through Sunday​ ​Less than 2 hours​ ​Turbidimetric Inhibition Immunoassay Method/Siemens Dimension
Marshfield​ Monday through Sunday​ Less than 2 hours​ Emit* 2000 Rate Assay/Beckman AU
​Beaver Dam​
​Monday through Sunday
​Less than 2 hours
​Turbidimetric Inhibition Immunoassay Method/ Siemens Dimension
Test Information
Collect trough specimen just prior to next dose. Half Life (adult): 70-100 hours. Time to steady state (adult): 15-25 days. Time to peak level: 4-10 hours. Coadministration with drugs that acidify urine (valproic acid, salicylate) will decrease excretion.​
Reference Range Information
Performing Location Reference Range
All Performing Sites Therapeutic:   10.0 – 20.0 μg/mL
See Critical Value List for list of current critical values​
Outreach CPTs
CPT Modifier
(if needed)		 Quantity Description Comments
80185 ​ ​ ​ ​ ​
Synonyms/Keywords
Dilantin, DPH, Diphenylhydantoin​
Ordering Applications
Ordering Application Description
​Centricity

​a. Dilantin (Phenytoin)

b. Phenytoin (Dilantin)

​Cerner ​Phenytoin Level Total
If the ordering application you are looking for is not listed, contact your local laboratory for assistance.
Specimen Requirements
Fasting Required Specimen Type Preferred Container/Tube Acceptable Container/Tube Specimen Volume Specimen Minimum Volume
(allows for 1 repeat)		 Pediatric Minimum Volume
(no repeat)
No​ Serum​ Serum Separator Tube (SST) ​Red Top Tube (RTT)​ 0.5 mL​ 0.2 mL​ 0.4 mL whole blood​
Collection Processing
Indicate time of collection.
Separate serum from cells within 1 hour of collection if using RTT.
Serum must be removed from gel within 24 hours of collection.
Specimen Stability Information
Specimen Type Temperature Time
Serum​ ​ ​ Room Temperature 8 hours
Refrigerate​ 7 days​
Frozen​ 30 days
Useful For
Phenytoin (5,5-diphenylhydantoin) is one of the most widely prescribed drugs for the treatment of seizure disorders. It is considered one of the drugs of choice for generalized major motor (grand mal epilepsy) and focal seizures. ​
Reference Range Information
Performing Location Reference Range
All Performing Sites Therapeutic:   10.0 – 20.0 μg/mL
See Critical Value List for list of current critical values​
For more information visit:
Performing Laboratory Information
Performing Location Day(s) Test Performed Analytical Time Methodology/Instrumentation
Weston​​ ​Monday through Sunday​ ​Less than 2 hours​ ​Turbidimetric Inhibition Immunoassay Method/Siemens Dimension
Marshfield​ Monday through Sunday​ Less than 2 hours​ Emit* 2000 Rate Assay/Beckman AU
​Beaver Dam​
​Monday through Sunday
​Less than 2 hours
​Turbidimetric Inhibition Immunoassay Method/ Siemens Dimension
For billing questions, see Contacts
Outreach CPTs
CPT Modifier
(if needed)		 Quantity Description Comments
80185 ​ ​ ​ ​ ​
For most current information refer to the Marshfield Laboratory online reference manual.