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Lab Manual for Moffitt-Long and Mount Zion

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Phenytoin, total

Item Value
Test Update Information Phenytoin assay changed from the Abbott Axsym method to the Beckman DxC method on 09/20/2012.
Approval req'd? No
Available Stat? Yes
Test code PHNY
Test group Phenytoin
Performed by Parnassus Chemistry
In House Availability Test available 24 hours per day 7 days per week
Method Turbidimetric inhibition immunoassay (Beckman DxC800)
Collection Instructions Time to steady state: 3-4 days

Collect samples 30 minutes before AM dose.

Draw at least 4 hours post-IV dose and 6-9 hours post-PO dose

Indicate time of draw on requisition.
Container type Red top
Amount to Collect 1 mL blood
Sample type Serum
Preferred volume 0.5 mL serum
Min. Volume 0.2 mL serum
UCSF Rejection Criteria Specimen received in gold top or lithium heparin tube with gel
Units mg/L
Normal range
Therapeutic: 10-20 mg/L


Source: Phenytoin: Drug information, Copyright 1978-2012 Lexicomp, Inc. Accessed in UpToDate, August 2012

Therapeutic ranges adopted or modified from the literature based on recommendations of UCSF Pharmacists
Critical value > 30 mg/L
Synonyms Dilantin; Fosphenytoin; Cerebyx
Stability Room temperature 8 hours, refrigerated 2 days, frozen at -20C 1 week
Turn around times STAT 1 hour, Routine 4 hours
Additional information The level of phenytoin can be empirically corrected for the effect of hypoalbuminemia with the formula:

Corrected = Measured/(0.9(actual albumin/4.4) + 0.1)

OR

Corrected = Measured/(0.2 x actual albumin) + 0.1).

If renal failure coexists with hypoalbuminemia, the formula is:

Corrected = Measured/(0.9)((0.48 x actual albumin/4.4) + 0.1)

OR

Corrected = Measured/(0.1 x actual albumin) + 0.1)

Click here for A guide on Drug Level Monitoring
LOINC code 3968-5
Last Updated 1/23/2013 3:48:52 PM
Entry Number 737
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