The University of Iowa (UIHC)
Department of Pathology
LABORATORY SERVICES HANDBOOK


Phenytoin, Free
Order Code: FDPH
Order Form: A-1a Therapeutic Drug Analysis or IPR Req
  Chemistry
6240 RCP
356-3527
Specimen
Plasma
Collection Medium:
Plasma separator tube
Alternate
Collection Media:
Call laboratory for additional acceptable specimen collection 
containers.
Minimum:
2 ml whole blood from light green top tube
Testing Schedule:
Monday-Friday, 0800-1200.
Analytic Time:
24 hours (upon receipt in laboratory)
Reference Range:
1.0-1.9 mcg/ml
Average percent free is 9.6% with a range of 7.0-14.6% (N=91).

Critical value: >1.9 mcg/ml
Comments:
Note:  Phenytoin plasma specimens should not be drawn for 2 hours 
following completion of an I.V. fosphenytoin infusion or 4 hours 
following an I.M. fosphenytoin dose (See Fosphenytoin).  To accurately
determine the percentage of free phenytoin, a total phenytoin should be 
ordered on the same sample.
Test
Limitations:
Criterion: recovery plus or minus 0.6 ug/ml of initial value at 
concentrations less than 6 ug/ml or plus or minus 10% of initial value 
at concentrations greater than 6 ug/ml.

Icterus: No significant interference from bilirubin up to an I index of 
30 (approximate bilirubin concentration: 60 mg/dl).

Hemolysis: No significant interference from hemoglobin up to an H index 
of 800 (approximate hemoglobin concentration: 1000 mg/dl).

Lipemia (Intralipid): No significant interference from lipemia up to an 
L index of 750. (approximate triglycerides concentration: 2000 mg/dl). 
There is poor correlation between turbidity and triglycerides 
concentration.
Methodology:
EIA (Enzymatic ImmunoAssay)
CPT Code:
80186
 
See also:
Phenytoin, Plasma
 
See Additional Information:
Chemistry Critical Lab Values

Alphabetic main page

Updated: 02/28/2007

Note: The information contained in this handbook is for use by personnel of University of Iowa Health Care. No other use is implied or intended.