Clinical Chemistry
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Clinical Chemistry 52: 2116-2117, 2006; 10.1373/clinchem.2006.072033
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(Clinical Chemistry. 2006;52:2116-2117.)
© 2006 American Association for Clinical Chemistry, Inc.

Letters to the Editor

Equimolar Ammonia Interference in Potassium Measurement on the Osmetech OPTI CCA: A Reply

Chao Lina and James K. Tusa

Osmetech Inc., Roswell, GA

aAddress correspondence to this author at: Osmetech Inc, 235 Hembree Park Drive, Roswell, GA 30076. Fax 770-510-4444; e-mail chao.lin@osmetech.com.

The first 20% of the full text of this article appears below.


To the Editor:

We agree that the Osmetech OPTI Critical Care Analyzer (OPTI) measurement of potassium ion shows a bias with samples containing extremely high plasma ammonia concentrations, as reported by Carayanopoulos et al. (1). As a result of this report we have notified all OPTI customers of this interference at these rare high ammonia concentrations.

Hyperammonemia has an estimated incidence in newborns of 1 per 25 000–53 000 live births (2)(3). Urea cycle disorders are the usual cause (4), occasionally leading to ammonia concentrations >400 µmol/L, which would increase the potassium reported on OPTI by 0.5 mmol/L. Such a bias is greater than allowed under the US Healthcare Financing Administration/CLIA proficiency testing criteria for acceptable performance (5). In rare cases, newborns may also suffer hyperammonemia attributable to other pathologies (6), such as organic acidemias, fatty acid oxidation disorders, congenital lactic acidosis, lysinuric protein intolerance, hepatic or renal dysfunction, . . . [Full Text of this Article]






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Copyright © 2006 by the American Association for Clinical Chemistry.