BACKGROUND: We encountered a case of bromism that was found to be due to pseudohyperchloremia. Hyperchloremia is known to be able to reveal existing bromism, but the fact that bromine (Br(-)) influences chloride (Cl(-)) in assays that use ion electrode machines is not widely known. METHODS: We assayed samples by an ion electrode method, using four types of machines. Different amounts of Cl(-) or Br(-) were added to each sample. RESULTS: With the addition of Cl(-) to the samples, the assayed Cl(-) concentrations were proportional to the amount of added Cl(-). With the addition of Br(-) to the samples, the assayed Cl(-) concentrations, as measured by all machines, were increased, but the amounts of the increase differed significantly, and were not proportional to the amount of Br(-) added. In particular, in the machine most markedly influenced by additional Br(-), the Cl(-) concentrations increased from 94.9 to 139.6 mEq/l with the addition of 10 mEq/l of Br(-). Conversely, in the least influenced machine, Cl(-) values increased from 95.0 to 103.0 mEq/l with the addition of 10 mEq/l of Br(-). CONCLUSION: The influence on the Cl(-) assay of the addition of Br(-) varied significantly between different ion electrode machines. Clinical nephrologists therefore need to be able to recognize the characteristics of the specific machines used in their hospitals.
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