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Clinical Chemistry 50: 2463-2464, 2004; 10.1373/clinchem.2004.039412
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(Clinical Chemistry. 2004;50:2463-2464.)
© 2004 American Association for Clinical Chemistry, Inc.

Letters to the Editor

Interference in Measurement of Potassium Caused by Bacterial Contamination of an Analyzer

John Shepherda and Brian Baldwin

1 Department of Clinical Biochemistry, Hull Royal Infirmary, Anlaby Road, Hull HU3 2JZ, United Kingdom

aAuthor for correspondence. Fax 44-482-607752; e-mail john.shepherd@hey.nhs.uk.

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


To the Editor:

We encountered a problem with potassium measurement after periods of standby on a Beckman Synchron LX20 Pro. Initial potassium measurements were rejected because of excessive reference drift, and potassium results for quality-control (QC) samples were as much as 2.5 mmol/L above the previous mean. Replicate analyses of control material immediately after standby revealed a decreasing trend in potassium concentration, whereas simultaneously determined electrolytes did not. When the analyzer had not been in standby, no such problems were seen.

We recorded the voltage from the analog-to-digital converter (ADC) during 10 replicate measurements of QC material immediately after an 8-h standby (Fig 1A ). The reference voltages increased progressively, whereas the potassium voltages did not. Because the difference between the sample and reference is used to calculate the potassium concentration, the reported potassium concentration decreased progressively (Fig. 1A ).


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  		Figure 1. Results of . . . [Full Text of this Article]






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