Phenytoin, Free

Label Mnemonic:	FDPH
Epic code:	LAB32
Downtime form:	A-1a Doctor/Provider Orders - Pathology Core and Specialty Care Nursery

Chemistry
6240 RCP
356-3527

Specimen(s):

Plasma

Collection Medium:

Plasma Separator Tube 4.5 mL

Alternate Collection Media:

Call laboratory for additional acceptable specimen collection containers.

Minimum:

3 mL whole blood from light green top tube or TWO Microtainer^® devices.

Testing Schedule:

Daily. Sample must be in the lab by 1200; results available by 1600.

Turn Around Time:

24 hours (upon receipt in laboratory)

Reference Range:

1.0-1.9 μg/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 μg/mL of initial value 
at concentrations less than 6 μg/mL or plus or minus 10% of 
initial value at concentrations greater than 6 μg/mL.

Methodology:

Homogeneous Enzyme Immunoassay

CPT Code:

80186