Phenobarbital Level
| Abbrev Code: | PHENO | ||
| Order Code: | LAB30 | Order Name: | Phenobarbital Level |
| Synonyms: | Also see Free Phenobarbital (FPHENO, LAB3482) | ||
| Methodology: | Roche: Kinetic interaction of microparticles in a solution (KIMS)
Vista: Turbidmetric rate Remisol: Homogenous enzyme immunoassay Architect: Chemiluminescent microparticle immunoassay (CMIA) |
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| CPT Codes: | 80184 x1, 80184 x1 | ||
| Turnaround Time: | Performed and reported 24 h/day. | ||
| Associated Links: | |||
Collection Instructions
| Specimen: | Blood |
| Optimal Volume: | 2.5 mL |
| Minimum\Peds Volume: | 0.8 mL |
| Container: | Red (no gel), St Johns/Woodwinds-Green (lithium heparin, no gel) Alternate Containers: Green (lithium heparin, no gel), Grand Itasca - Green (lithium heparin, no gel), Purple (EDTA), St Johns/Woodwinds - Red (no gel) |
| Collection Instructions: | Trough level is preferred; collect immediately before dose. It is advisable to monitor at the same time in the dosing schedule. |
| Causes for Rejection: | Collection in a gel tube. |
Processing and Shipping
| Specimen Processing: | Centrifuge and aliquot 1.25 mL, 0.3 mL minimum. Store in room temperature up to 48 hours. Alternatively, refrigerate. |
| Shipping Instructions: | Ship at room temperature to arrive within 48 hours. Alternatively, ship at refrigerated temperature. |
| Stability: | 7 days at room or refrigerated temperature; 1 year frozen. |
| Test Performed at or Referral Lab | Chemistry (Grand Itasca, Range, Roche-UMMC East, Southdale, UMMC West Bank) |
Interpretive
| Critical Range: | Greater than 50 mg/L |
| Therapeutic Range: | Roche: 10-30 μg/mL
Vista: 15-40 mg/L Grand Itasca: 10-40 ug/mL The therapeutic range of phenobarbital is correlated with seizure control as well as the absence of toxic effects, and is generally accepted to be between 10 and 30 μg/mL. Variation in metabolism and absorption of the drug may cause levels to rise above 40 μg/mL or fall below 15 μg/mL. The most frequent dose related side effect is sedation, to which a tolerance usually develops. Phenobarbital serum levels above 40 μg/mL are often associated with nystagmus, ataxia and dysarthria. At high doses, phenobarbital can cause an increase in seizure frequency. |
| Use: | Monitor therapeutic drug level of phenobarbital; use with primidone levels to monitor therapeutic drug level of primidone; evaluate phenobarbital toxicity. Half-life is 50-120 h (adult); and 40-70 h (child). |
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