| A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # |
Phenytoin
MessagePerforming Lab: Lakeview, Regions, Westfields
Test Code
0200
Alias/See Also
Sunquest: PHEN; Dilantin, Phenytoin Total
CPT Codes
80185
Includes
Time of Last Dose, Phenytoin
Preferred Specimen
0.2 mL Lithium Heparin Plasma (light green-top) tube
Minimum Volume
0.1 mL
Other Acceptable Specimens
Serum (gold-top, red-top, red/gray-top), Lithium Heparin (light green-top) on ICE
Instructions
Collection:
Phenytoin specimens should be drawn just before the next dose for trough levels. If toxicity is suspected, specimens may be drawn at any time.
Phenytoin specimens should be drawn just before the next dose for trough levels. If toxicity is suspected, specimens may be drawn at any time.
Transport Temperature
Refrigerated
Specimen Stability
Room Temperature: 8 hours
Refrigerated: 7 days
Frozen: 2 months
Refrigerated: 7 days
Frozen: 2 months
Methodology
Multi-point immuno-rate
Setup Schedule
Daily
Report Available
Same day
Limitations
Specimens with an elevated Total Protein (>9.0 g/dL) may give a positive bias. The degree of protein binding may vary from patient to patient. Such factors can confuse interpretation of measured concentrations of the drug.
Since the clinical signs of toxicity are correlated with the concentration of unbound drug, some patients will achieve adequate control of seizures without evidence of toxicity only when the total concentration of phenytoin is above the usual therapeutic range.
Since the clinical signs of toxicity are correlated with the concentration of unbound drug, some patients will achieve adequate control of seizures without evidence of toxicity only when the total concentration of phenytoin is above the usual therapeutic range.
Reference Range
10 - 20 µg/mL
Critical: >= 30 µg/mL
Critical: >= 30 µg/mL
Clinical Significance
Phenytoin is a widely prescribed anticonvulsant drug used in the treatment of generalized and partial seizures. Phenytoin measurements are used to monitor patient compliance and therapy and to diagnose potential overdose. Only the free portion of Phenytoin is capable of crossing biologic membranes and interacting at important binding sites. Since the degree of protein binding can be affected by the presence of other drugs and altered physiological states, free drug determinations represent an important too for customizing individual patient anticonvulsant levels.
