valproic acid in serum/plasma
Indications
monitoring of valproate therapy
Reference interval
Therapeutic valproic acid concentrations vary significantly depending on the individual patient. Published information sources say that a range of 50-100 ug/mL may indicate effective serum concentration for many patients; however, some individuals are best treated at concentrations outside this range. Concentrations greater than 100 ug/mL are often associated with toxic symptoms. The physician must determine the appropriate therapeutic range for each patient.
Principle
The VALP pack is used in the DuPont ACA discrete clinical analyzer to quantitatively measure valproic acid, an anti-epileptic drug in serum & plasma. It is an adaptation of Syva's homogeneous enzyme immunoassay technique, EMIT. The reagents used in this methodology are matched lots of valproic acid antibody & the valproic acid-glucose-6-phosphate dehydrogenase conjugate. The concentration of valproic acid determines the amount of valproic acid-glucose-6-phosphate dehydrogenase (VALP-G6PD) conjugate that is bound to the valproic acid antibody. The unbound conjugate catalyzes the oxidation of glucose-6-phosphate, with the simultaneous reduction of NAD to NADH, more rapidly than does the bound conjugate. The rate of increasing absorbance at 340 nm due to the increase in NADH is related to the concentration of valproic acid by means of a calibration curve or a mathematical function.
Clinical significance
Valproic acid is a recent addition to the list of drugs used in the treatment of epilepsy. Its anticonvulsant effects were discovered in 1963. It is useful in the control of many types of seizures, especially simple & complex absence seizures. Some authorities also consider it to be the drug of first choice in generalized motor seizures & myoclonic seizures.
See valproic acid for adverse effects (toxicity)
Specimen
Patient preparation: No special patient preparation is required.
Collect blood samples by venipuncture following established good laboratory practices. If the sample is obtained through the infusion set, flush the line thoroughly with saline before taking the blood sample. With some exceptions, any anticoagulant may be used to collect plasma for analysis. Serum, as well as plasma, may be used for most assays. If is very important that the physician be informed of the times of sample collection & dose administration; this information should be supplied to the laboratory with each sample & reported with the results of each test. Samples derived from blood should be refrigerated upon collection & stored frozen (-20 degrees Celsius or colder) if not analyzed within 24 hours. Complete mixing of each thawed sample is required before analysis.
More general terms
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Additional terms
Component of
References
- ↑ ACA IV Discrete Clinical Analyzer Instrument Manual, Volume 1: Operation, DuPont Company, Wilmington, Delaware, 1984.
- ↑ ACA IV Discrete Clinical Analyzer Instrument Manual, Volume 3B: Chemistry, DuPont Company, Wilmington, Delaware, 1984.
- ↑ Valproic Acid Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0090290.jsp
- ↑ Panel of 3 tests Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0099310.jsp