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Salicylate Intoxication as a Cause of Pseudohyperchloremia

2008; Elsevier BV; Volume: 51; Issue: 2 Linguagem: Inglês

10.1053/j.ajkd.2007.11.017

1523-6838

Brian W. Zimmer, Richard J. Marcus, K. F. Sawyer, Fred Harchelroad,

Antibiotics Pharmacokinetics and Efficacy

Two patients were recently admitted to our institution with similar presentations of apparent salicylate overdose. Both patients presented with serum electrolyte and blood gas values suggestive of acute respiratory alkalosis with metabolic compensation. Unexpectedly, both patients were found to have significantly elevated serum chloride values on presentation of 174 mEq/L (mmol/L) and 146 mEq/L (mmol/L) with salicylate levels of 8.1 mg/L (0.06 mmol/L) and 4.5 mg/L (0.03 mmol/L), respectively. Anion gaps were calculated to be −49 mEq/L (mmol/L) and −26 mEq/L (mmol/L). Bromide levels were undetectable in both cases. Serial analyses of serum chloride versus salicylate level for both patients are shown in Fig 1. As seen in these cases, salicylates can potentially represent another cause for falsely elevated chloride levels and thus an extremely negative anion gap. Although salicylate poisoning by itself can cause an increase in chloride level,1Routh J.I. Paul W.D. Assessment of interference by aspirin with some assays commonly done in the clinical laboratory.Clin Chem. 1976; 22: 837-842PubMed Google Scholar the magnitude of the increase in these cases suggests another potential cause. In our patients, serum electrolyte results were determined with a Roche Cobas Integra 800 ion-selective electrode (ISE) module (Roche Diagnostic, F. Hoffmann-La Roche, Ltd, Basel, Switzerland). Although the sodium and potassium electrodes of this model have been shown to be consistently reliable, there have been a number of reports of falsely high chloride concentrations.2Wang T. Diamandis E.P. Lane A. Baines A.D. Variable selectivity of the Hitachi chemistry analyzer chloride ion-selective electrode toward interfering ions.Clin Biochem. 1994; 27: 37-41Crossref PubMed Scopus (20) Google Scholar, 3Mori L. Waldhuber S. Salicylate interference with the Roche Cobas Integra chloride electrode.Clin Chem. 1997; 43: 1249-1250PubMed Google Scholar, 4Faulkner A.M. Peake M.J. Bicarbonate interference with Hitachi chloride electrodes.Ann Clin Biochem. 1991; 28: 107-108PubMed Google Scholar Falsely high values had previously been caused by a general low selectivity of the chloride electrode, which can respond to other ions such as iodide, thiocyanate, nitrate, and bromide. The potential for an additional interaction with salicylates has recently been elucidated in the chemistry literature. Mori et al3Mori L. Waldhuber S. Salicylate interference with the Roche Cobas Integra chloride electrode.Clin Chem. 1997; 43: 1249-1250PubMed Google Scholar had previously reported on this potential interference using the Integra 800 ISE and demonstrated a linear relationship between chloride values and salicylate concentrations using stock salicylate solution. At our institution, the Integra 800 ISE has only been used since March 2007. The data from our patients shown in Fig 1 demonstrate a fairly linear relationship between salicylate concentrations and chloride values, much as Mori et al had earlier postulated using standards. This potential interaction also appears to be dependent on the "age" of the electrode itself. Although Roche continues to advise that the chloride ISE should be changed every 3 months, they urge a more frequent replacement dependent on the use of the electrode itself, possibly every 4 weeks.3Mori L. Waldhuber S. Salicylate interference with the Roche Cobas Integra chloride electrode.Clin Chem. 1997; 43: 1249-1250PubMed Google Scholar Braun et al5Braun S.L. Ciolek K. Vogt W. Early detection of the selectivity loss of the Cobas Integra analyzer chloride ion-selective electrode.Clin Chem. 2004; 50: 1272-1273Crossref PubMed Scopus (5) Google Scholar reported findings using the Integra ISE in an attempt to quantify the duration to loss of selectivity on an "aging" electrode and recommended use of a selectivity control solution to help achieve maximum useful lifetime of the electrode. In our patients, it is interesting to note that the chloride electrodes had been in use for at least 5 weeks. In conclusion, salicylate toxicity should be considered as another potential cause of pseudohyperchloremia. Letters to the Editor may be in response to an article in AJKD or may concern a topic of interest to currentnephrology. For responses to AJKD articles, the Letter must be received no more than 6 weeks after the article's date of print publication. The body of the letter should be as concise as possible and in general should not exceed 250 words. Up to 10 references and 1 figure or table may be included. There is no guarantee that letters will be published. Letters are subject to editing and abridgment without notice.Letters should be submitted via AJKD's online manuscript handling site, http://www.editorialmanager.com/ajkd. More information, including details about how to contact the editorial staff for assistance, is available in the journal's Information for Authors. Letters to the Editor may be in response to an article in AJKD or may concern a topic of interest to currentnephrology. For responses to AJKD articles, the Letter must be received no more than 6 weeks after the article's date of print publication. The body of the letter should be as concise as possible and in general should not exceed 250 words. Up to 10 references and 1 figure or table may be included. There is no guarantee that letters will be published. Letters are subject to editing and abridgment without notice. Letters should be submitted via AJKD's online manuscript handling site, http://www.editorialmanager.com/ajkd. More information, including details about how to contact the editorial staff for assistance, is available in the journal's Information for Authors. Support: None. Financial Disclosure: None.