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Unit Code 81771:
Valproic Acid, Free and Total, Serum

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Method Description

Enzyme-multiplied immunoassay technique (EMIT) performed using

Olympus analyzer:EMIT offers an alternative to the traditional

spectroscopic and chromatographic method for quantitating blood

concentrations of drugs. The technique for drugs is based upon

an enzymatic assay for glucose-6-phosphate dehydrogenase,

using spectral properties at 340 nm, in which the reduction of nicotinamide

adenine dinucleotide (NAD) substrate is monitored. The basis of the

drug detection technique is an immunological reaction between the

drug and a specific antibody. The reagent contains the enzyme

(glucose-6-phosphate dehydrogenase) to which the drug is covalently

bound and antibody-specific to the drug. The antibody binds most of the

drug-bound enzyme, rendering the enzyme inactive. This results

in a baseline enzymatic activity. In the presence of free drug, antibody

equilibrates between free drug and enzyme-bound drug leaving

some of the drug-bound enzyme uncomplexed and able to catalyze

the reaction. If more free drug is introduced, either as standard or

sample, then competition for the antibody takes place between the

drug in the sample and the drug attached to the enzyme. This

results in more drug-bound enzyme being left uncomplexed and

able to catalyze the enzyme reaction at a greater rate as

compared to the baseline activity. The observed enzyme activity

increases with the amount of total free drug in the sample. (Moyer TP:

Therapeutic drug monitoring. In Tietz Textbook of Clinical Chemistry.

4th edition. Edited by CA Burtis, ER Ashwood. WB Saunders

Company, Philadelphia, 2005, pp 1237-1285)

Performing Laboratory Location

Rochester

Key