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
 
See also:
Phenytoin, Plasma
 
See Additional Information:
Chemistry Critical Lab Values