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22773 Phenytoin, Free

Phenytoin, Free
Test Code: PTN-F
Synonyms/Keywords
​Dilantin, Free Phenytoin
Useful For
​Assessing therapeutic levels of phenytoin to optimize patient's dose and to assess toxicity and compliance
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)​ 2 mL​ 1 mL​ 1 mL​
Collection Processing Instructions
Indicate time of collection.
Serum must be removed from gel within 24 hours of collection.
Preferable to prepare ultra-filtrate as soon as possible after 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
Marshfield​ Monday through Sunday 1 day​ Emit* 2000 Rate Assay/Beckman AU
Test Information
Phenytoin (Dilantin) is one of the most widely prescribed anticonvulsants and is occasionally used as a myocardial antiarrhythmic.  Due to the fact that phenytoin is highly bound to serum proteins (89-95%), any alteration to the protein binding of phenytoin due to uremia, hypoalbuminemia, ingestion of other drugs, or age can result in significantly different clinical response to total phenytoin concentration.  Only the free drug is small enough to pass through capillary membranes and reach the site of action.  When a patient's clinical response does not agree with the total drug concentration, or the protein binding of a patient is believed to be abnormal, the free drug level may correlate more accurately with the clinical effectiveness or toxicity of the drug.   ​
Reference Range Information
Performing Location Reference Range
​Marshfield Negative.  Positives are reported with a quantitative result.​
Interpretation

​Therapeutic Range:  1.0 - 2.0 ug/mL

Outreach CPTs
CPT Modifier
(if needed)		 Quantity Description Comments
​80186 ​ 1​ ​ ​
Synonyms/Keywords
​Dilantin, Free Phenytoin
Ordering Applications
Ordering Application Description
​Centricity ​Phenytoin, Free
​Cerner ​Phenytoin Level Free
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)​ 2 mL​ 1 mL​ 1 mL​
Collection Processing
Indicate time of collection.
Serum must be removed from gel within 24 hours of collection.
Preferable to prepare ultra-filtrate as soon as possible after collection.
Specimen Stability Information
Specimen Type Temperature Time
Serum​ ​Room Temperature 8 hours
Refrigerate 7 days
Frozen 30 days
Useful For
​Assessing therapeutic levels of phenytoin to optimize patient's dose and to assess toxicity and compliance
Reference Range Information
Performing Location Reference Range
​Marshfield Negative.  Positives are reported with a quantitative result.​
Interpretation

​Therapeutic Range:  1.0 - 2.0 ug/mL

For more information visit:
Performing Laboratory Information
Performing Location Day(s) Test Performed Analytical Time Methodology/Instrumentation
Marshfield​ Monday through Sunday 1 day​ Emit* 2000 Rate Assay/Beckman AU
For billing questions, see Contacts
Outreach CPTs
CPT Modifier
(if needed)		 Quantity Description Comments
​80186 ​ 1​ ​ ​
For most current information refer to the Marshfield Laboratory online reference manual.