Unexplained Bromide Toxicity Presenting as Hyperchloremia and a Negative Anion Gap

A high serum bromide level can cause erroneously high serum chloride levels measured through routine assays. Here, we describe a case of pseudohyperchloremia in which routine labs showed a negative anion gap and elevated chloride levels measured with ion-selective assay. The serum chloride level was found to be lower when measured with a chloridometer that employs a colorimetric method of quantification. The initial serum bromide level was elevated at 1100 mg/L that was confirmed by repeating the test that again showed an elevated level of 1600 mg/L and appeared to cause erroneous hyperchloremia when using conventional serum chloride quantification methods. Our case highlights lab errors and factitious hyperchloremia as a cause of the negative anion gap caused by bromism, even without a clear history of bromide exposure. The case also underscores the importance of chloride measurement using both colorimetric methods and ion-selective assay in the case of hyperchloremia.