Phenytoin, Free, Plasma

Phenytoin, Free

Order Code:	FDPH
Epic Lab Code:	LAB32
Order Form:	A-1a Therapeutic Drug Analysis or Epic 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:

3 mL whole blood from light green top tube or TWO microtainers.

Testing Schedule:

Monday-Friday. Sample must be in the lab by 1200; results available by 1500.

Turn Around 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).

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