Phenytoin/Free Phenytoin

Test Code

LAB4072

Alias/See Also

PTN/ Free PTN;Dilantin/Free Dilantin

Preferred Specimen

4.5 ml (4.5 ml min) lithium heparin (green); alternate-SST (gold) or Red (no additive)

Minimum Volume

2 ml plasma; alternate-serum

Other Acceptable Specimens

Gold SST

Instructions

Separate from cells ASAP. After centrifugation, if not in gel barrier tube, pour off plasma into an aliquot tube

Transport Temperature

Room Temp

Specimen Stability

Separated from cells: 1 month refrigerated

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)

Icteric: >30 mg/dL bilirubin, Hemolysis: >800 mg/dL hemoglobin, Lipemia: >750 mg/dL triglycerides

Methodology
Fluorescent Polarization Immunoassay (FPIA), Immunoassay

Setup Schedule

Mon- Sun

Reference Range

Reference Range 1.0-2.0 μg /ml
Toxic >/= 3.0 μg /ml

Clinical Significance

The total concentrations of the drug in the blood consist of the protein-bound fraction and the free fraction, of which only the free
drug is considered to be pharmacologically active. Due to the fact that phenytoin is highly bound to plasma proteins (89-95%),
any alteration in the protein binding of phenytoin due to uremia, hypoalbuminemia, and ingestion of other drugs or age can result
in a significantly different clinical response to a total phenytoin

Performing Laboratory
Piedmont Athens Regional

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.