Clinical Lab Handbook

Container/Tube: SST

Alternate Container: Red Top

Specimen Volume: 5 mL of serum

Collection Instructions: Allow specimen to clot for 30 minutes. Spin specimen in centrifuge.

Centrifuge specimens and remove the serum from the cellular material within 4 hours of collection

Enzyme-Multiplied Immunoassay Technique (EMIT®)

The VITROS VALP Reagent is a dual chambered package containing ready-to-use liquid reagents that are used in a twostep reaction to quantitatively measure valproic acid. Test sample is added to Reagent 1 containing antibody reactive to valproic acid, glucose-6-phosphate and nicotinamide adenine dinucleotide (NAD), followed by Reagent 2 containing valproic acid labeled with the enzyme glucose-6-phosphate dehydrogenase (G6P-DH). The assay is based on competition between valproic acid in the sample and valproic acid labeled with G6P-DH for antibody binding sites. G6P-DH activity decreases upon binding to the antibody, so valproic acid concentration in the sample can be measured in terms of G6P-DH activity. G6PDH converts NAD+ to NADH, resulting in an absorbance change that is measured spectrophotometrically at 340 nm. Endogenous serum G6P-DH does not participate in the reaction since NAD+ functions only with the bacterial (Leuconostoc mesenteroides) enzyme conjugate employed in the assay.

Valproic acid is used as sole or adjunctive therapy in the treatment of simple and complex absence seizures, and adjunctively in patients with multiple seizure types, which include absence seizures. High concentrations of valproic acid may lead to central nervous system depression, tremor, and thrombocytopenia. Very high concentrations of valproic acid may also increase the risk of developing fatal hepatotoxicity, stupor, coma, or cerebral edema. Valproic acid is extensively metabolized by the liver. Other coadministered drugs, including other antiepileptics, may induce or inhibit the drug metabolizing enzymes of the liver. When these drugs are added or removed from the therapeutic regimen of a patient, the clearance and concentration of valproic acid may be altered, requiring dosage adjustment. Serum or plasma valproic acid measurements are used in the diagnosis and treatment of valproic acid overdose and in monitoring levels of valproic acid to ensure appropriate therapy.

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Note: Peak specimen should be drawn 1 to 3 hours after the dose is given. Trough specimen should be drawn just prior to next dose.