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HelpTest Code LAB301 Phenytoin, Plasma or Serum
Additional Codes
| Test Name in EPIC | EPIC Test Code | Mnemonic |
|---|---|---|
| PHENYTOIN | LAB301 | DILAN |
Useful For/Utility
Use for the quantitative measurement of phenytoin in human serum or plasma. The measurements obtained are used in the diagnosis and treatment of phenytoin overdose and in monitoring levels of phenytoin to help ensure appropriate therapy.
Methodology
Chemiluminescent Microparticle Immunoassay (CMIA)
Blood levels of phenytoin reflect only a total serum concentration of the drug. Only free unbound phenytoin has biological activity. Population groups that are predisposed to elevated free phenytoin levels include neonates, elderly persons, and individuals with uremia, hypoalbuminemia, or hyperbilirubinemia. These patients may exhibit toxicity when drug levels are within the therapeutic range. If desired, an adjusted dilantin level which corrects for low albumin is available (#LAB3708 Phenytoin, Adjusted, Plasma or Serum).
Clinical Information
Monitoring phenytoin concentrations, along with careful clinical assessment, is the most effective means of improving seizure control, reducing the risk of toxicity, and minimizing the need for additional anticonvulsant medication for the following reasons:
Phenytoin concentrations correlate better with pharmacologic activity than does dosage because of individual differences in absorption, metabolism, disease states, concomitant medication, and compliance. Concentration monitoring helps physicians individualize dosage regimens.
The hepatic enzyme system for metabolizing phenytoin can become saturated within the drug’s therapeutic range. When this occurs, small dosage alterations can lead to unexpected drug accumulation and clinical toxicity.
Phenytoin is safe and effective only in a narrow range of concentrations.
Specimen Requirements
Specimen must be refrigerated until test is performed.
Submit only 1 of the following specimens:
Preferred:
Specimen Type: Plasma
Container/Tube: Light-green top (lithium heparin gel)
Specimen Volume: 1 mL
Specimen Minimum Volume: 0.5 mL
Collection Instructions:
1. Spin down, separate plasma from cells within 2 hours of draw.
2. If plunger filters are used, immediate removal of plasma is indicated unless an air gap can be created between the device and specimen.
3. For oral dose, draw trough level unless otherwise specified. To monitor effect of oral loading dose, draw level 24 hours post dose. For intravenous (IV) dose, draw trough level, 30 minutes prior to next dose. To monitor effect of IV loading dose, draw 2 to 4 hours after dose is infused and complete. If toxicity is suspected, draw level when ordered STAT.
Additional Information:
1. Avoid repeated freeze/thaw cycles.
2. If extreme lipemia-use ultracentrifuged specimen.
3. Label specimen appropriately (plasma).
Alternate:
Specimen Type: Serum
Container/Tube: Serum gel
Specimen Volume: 1 mL
Specimen Minimum Volume: 0.5 mL
Collection Instructions:
1. Spin down, separate serum from cells within 2 hours of draw.
2. If plunger filters are used, immediate removal of serum is indicated unless an air gap can be created between the device and specimen.
3. For oral dose, draw trough level unless otherwise specified. To monitor effect of oral loading dose, draw level 24 hours post dose. For intravenous (IV) dose, draw trough level, 30 minutes prior to next dose. To monitor effect of IV loading dose, draw 2 to 4 hours after dose is infused and complete. If toxicity is suspected, draw level when ordered STAT.
Additional Information:
1. Avoid repeated freeze/thaw cycles.
2. If extreme lipemia-use ultracentrifuged specimen.
3. Label specimen appropriately (serum).
Specimen Transport Temperature
Refrigerate 5 days/Ambient 2 days OK/Frozen OK
Day(s) Test Set Up
Monday through Sunday
Performing Laboratory
Chemistry-
St. Joseph's Medical Center Lab
Deer River Hospital Lab, Northern Pines Lab, Sandstone Hospital Lab, SMDC Clinical Lab, St. Mary's Hospital - Superior Lab, Virginia Hospital Lab, Moose Lake Hospital Lab
Fosston Hospital Lab, St. Mary's - Detroit Lakes Hospital Lab
Test Classification and CPT Coding
80185
Reference Values
10-20 µg/mL