Pseudohyperchloremia caused by the long-term use of phenobarbital and sodium bromide compound tablets: a case report

Serum chloride (Cl^-), which is an important analyte that reflects the electrolyte and acid-base balance in humans, is affected by several specific agents or substances. It has been reported that the abuse of bromine-containing drugs, such as bromvalerylurea may lead to pseudohyperchloremia, which is very rare yet, caused by the treatment dose of bromine-containing drugs. In this case report, we describe an epilepsy patient whose serum Cl^- was falsely elevated due to the long-term use of phenobarbital and sodium bromide compound tablets. We also discuss the anti-interference capacity of different analyzers and the disturbance of bromide-containing drugs in Cl^- determination.

A 34-year-old woman diagnosed with epilepsy for 11 years was admitted to our hospital for further treatment. She had increasingly frequent loss of consciousness and seizures. Her medication history included carbamazepine, levetiracetam, phenobarbital and sodium bromide compound tablets. The video electroencephalogram (VEEG) was moderately abnormal. No obvious abnormality was found in blood routine test, liver and kidney function, except an aberrantly elevated serum Cl^- level of 130 mmol/L; however, the patient did not present with the relevant signs and symptoms of hyperchloremia, such as thirst, fatigue, nausea and vomiting. Subsequently, we used three different analyzers to determine her Cl^- level and obtained the following results: an arterial blood Cl^- level of 107 mmol/L; a serum Cl^- level of 112 mmol/L; and no result. Reviewing her medical history, we discovered that the patient had been taking phenobarbital and sodium bromide compound tablets for 6 months to treat her seizures. Her serum bromide was 4.89 mmol/L, which may cause pseudohyperchloremia. After changing her treatment to phenobarbital tablets, her serum Cl^- returned to the normal range (106 mmol/L).

Bromide-containing drugs can cause a falsely elevated Cl^- level. When pseudohyperchloremia is suspected, different methods or instruments should be used to measure Cl^- levels.