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HelpTest Code LAB9106 Valproic Acid, Free, Serum
Additional Codes
VALPF
Useful For
Monitoring free valproic acid in therapy
Assessing compliance
Evaluating potential toxicity
Method Name
Ultrafiltration Followed by Immunoassay
Specimen Type
SerumSpecimen Required
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 2 mL
Collection Instructions:
1. Serum gel tubes should be centrifuged within 2 hours of collection.
2. Red-top tubes should be centrifuged, and the serum aliquoted into a plastic vial within 2 hours of collection.
Specimen Minimum Volume
1 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Serum | Refrigerated (preferred) | 14 days | |
| Frozen | 28 days | ||
| Ambient | 72 hours |
Reject Due To
| Gross hemolysis | Reject |
Reference Values
Therapeutic: 5-25 mcg/mL
Critical value: >30 mcg/mL
Interpretation
The generally acceptable range for total valproic acid used as a reference to guide therapy is 50 to 125 mcg/mL. The corresponding range of free valproic acid concentration for clinical reference is 5 to 25 mcg/mL.
Low free valproic acid concentration relative to these ranges may suggest inadequate dosing, whereas a high free valproic acid concentration may be associated with toxic effects.
Because the concentration of valproic acid fluctuates considerably depending on the time from last dose, interpretation of the clinical significance of the valproic acid concentration must take into consideration the timing of the blood specimen. For this reason, 2 collections are sometimes made to assess the trough and peak concentrations.
Method Description
The assay is based on a homogeneous enzyme immunoassay technique used for the quantitative analysis of valproic acid (free and protein-bound) in human serum or plasma. The assay is based on competition between drug in the sample and drug labeled with the enzyme glucose-6-phosphate dehydrogenase (G6PD) for antibody binding sites. Enzyme activity decreases upon binding to the antibody, so the drug concentration in the sample can be measured in terms of enzyme activity. Active enzyme converts oxidized nicotinamide adenine dinucleotide (NAD+) to NADH, resulting in an absorbance change that is measured spectrophotometrically. Endogenous serum G6PD does not interfere because the coenzyme functions only with the bacterial (Leuconostoc mesenteroides) enzyme employed in the assay.(Package insert: Valproic acid reagent. Roche Diagnostics; 04/2018)
Day(s) Performed
Monday through Sunday
Report Available
Same day/1 dayPerforming Laboratory
Mayo Clinic Laboratories in Rochester
CPT Code Information
80165
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| VALPF | Valproic Acid, Free, S | 4087-3 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| VALPF | Valproic Acid, Free, S | 4087-3 |
Forms
If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.