Specimen

Plasma

Collection Medium:

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