The Effect of Sample Handling on Free Valproic Acid Levels.

Document Type

Article

Publication Date

4-29-2021

Publication Title

The journal of applied laboratory medicine

Abstract

BACKGROUND: Valproic acid (VPA) is a broad-spectrum anticonvulsant drug. Under normal conditions, this drug is highly protein bound. However, in patients with hypoalbuminemia, the free fraction can increase substantially while the total VPA levels remain in therapeutic range. The neurologic activity and toxicity of the drug are directly related to free drug levels.

METHODS: Our in-house free VPA assay was validated using 20 patient samples obtained from a reference laboratory (RL1). It was further evaluated by parallel testing with RL1 using samples collected from our patients. Subsequently, sample handling effects were investigated by comparing free VPA levels measured in our laboratory to 3 selected RLs with different sample transportation conditions.

RESULTS: No significant bias was observed between the in-house assay (y) and RL1 (x) assay in free VPA measurement (y = 1.12x + 0.072, r = 0.994). However, patient samples collected in our institution and sent to RL1 revealed significant negative bias (y = 0.776x - 3.861, r = 0.954). A large discrepancy in free VPA levels was further observed from identical aliquots of the same samples transported to 3 RLs in different conditions.

CONCLUSIONS: Our study demonstrated that sample handling has significant impact on free VPA levels. The observed magnitude of variation exceeds a clinically acceptable limit and could alter clinical decisions.

Volume

6

Issue

3

First Page

645

Last Page

653

DOI

10.1093/jalm/jfaa181

ISSN

2576-9456

PubMed ID

33249432

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