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Test ID: Valproic Acid Level
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Valproic Acid Level
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Useful For
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Monitoring and adjusting Valproic acid concentration during therapy.
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Method name and description
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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 (G6PDH) 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 G6PDH does not interfere because the coenzyme functions only with the bacterial (Leuconostoc mesenteroides) enzyme employed in the assay.
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Clinical information
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Valproic acid (VPA; 2‑propylpentanoic acid; Depakene) is a relatively new anticonvulsant medication which is used chiefly for the treatment of primary and secondary generalized seizures, but is also effective against absence seizures. It is particularly effective in myoclonus, and is the drug of choice in photosensitive epilepsy.
At therapeutic concentrations, over 90 % of VPA in the circulation is bound to plasma proteins, primarily albumin. Binding is saturable, and at high VPA concentrations, the free fraction increases.
VPA has the fewest adverse effects of all the widely‑used anti‑epileptic agents. The most common side effects are gastrointestinal disturbances such as nausea and vomiting. Some incidences of tremor, coma or stupor have been noted; these often occur in conjunction with co‑administration of other anti‑epileptic drugs.
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Specimen type / Specimen volume / Specimen container
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Specimen type: Serum, Plasma
Minimum volume of sample: 1 mL
Serum: Plain tube (red or yellow top)
Plasma: Li‑heparin tube
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Collection instructions / Special Precautions / Timing of collection
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Collect blood by standard venipuncture techniques as per specimen requirements. When processing samples in primary tubes (sample collection systems), follow the instructions of the tube manufacturer
Specimens for valproic acid analysis should be drawn just prior to dose preferebly in the fasting state.
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Storage and transport instructions
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Storage: 2 days at 20 – 25°C
7 days at 4 – 8°C
3 months at ‑20 °C
Transport: 4-25°C
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Specimen Rejection Criteria
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Grossly hemolyzed, icteric and lipemic samples, wrong collection container, insufficient sample
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Biological reference intervals and clinical decision values
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Therapeutic Range: 347 - 693 umol/L
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Factors affecting test performance and result interpretation
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In very rare cases, gammopathy, in particular type IgM (Waldenstrom’s) macroglobulinemia may cause unreliable results.
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Turnaround time / Days and times test performed / Specimen retention time
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Daily (24/7)
Turn-around time:
STAT: 1 hour
Routine: One working day
Specimen Retention: 4 days
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