Low anion gap resulting from unexplained exposure to bromide in a patient with renal amyloidosis

Potential inaccuracies in chloride measurements in patients with severe metabolic acidosis

Background. To address the cause(s) of the significant differences in chloride (Cl⁻) concentrations between point-of-care blood gas analyzers and central laboratory analyzers. Methods. Cl⁻ concentrations measured simultaneously by a blood gas analyzer (ABL800 FLEX) and a central laboratory analyzer (Hitachi7600) were collected in patients with severe acidemia (pH < 7.20) (n = 32) and were examined for correlations between differences in Cl⁻ and factors associated with the acid-base status. Cl⁻ concentrations were measured with both analyzers for samples with different concentrations of lactate, inorganic phosphate, or bicarbonate (HCO₃⁻). Results. The differences in Cl⁻ concentrations were correlated with HCO₃⁻ concentrations (r = 0.72, P < 0.0001) and anion gap (r = 0.69, P < 0.0001). Only the addition of HCO₃⁻ proportionately increased Cl⁻ levels measured by a Hitachi7600, but it did not affect those measured by an ABL800FLEX. Conclusion. Cl⁻ measurements with some analyzers may be influenced by HCO₃⁻ concentrations, which could result in the observed discrepancies.

Severe metabolic alkalosis due to the combination of unmeasured cations and hypochloraemia in a patient with gastroparesia and frequent emesis

This report describes a patient with gastroparesia and frequent emesis admitted with severe metabolic alkalaemia, hyperlactataemia and acute renal failure. Metabolic alkalaemia was not only due to hypochloraemia but also due to unmeasured cations. These cations were found to be present by calculating anion gap and strong ion gap (both were negative, which is rare). After massive gastric bleeding the patient had a cardiac arrest; following cardiopulmonary resuscitation and infusion of a large volume of normal saline, new blood tests revealed improvement in chloraemia but also a significant increase in the anion gap, suggesting that unmeasured anions rapidly overcame unmeasured cations. The patient died after sequential episodes of cardiac arrest. Anion gap and strong ion gap were useful in the diagnosis of this "hidden" unusual cause of metabolic alkalosis and also in the diagnosis of metabolic acidosis after cardiac arrest, even with normal/high values of base excess and bicarbonate.

Serum Anion Gap: Its Uses and Limitations in Clinical Medicine

The serum anion gap, calculated from the electrolytes measured in the chemical laboratory, is defined as the sum of serum chloride and bicarbonate concentrations subtracted from the serum sodium concentration. This entity is used in the detection and analysis of acid-base disorders, assessment of quality control in the chemical laboratory, and detection of such disorders as multiple myeloma, bromide intoxication, and lithium intoxication. The normal value can vary widely, reflecting both differences in the methods that are used to measure its constituents and substantial interindividual variability. Low values most commonly indicate laboratory error or hypoalbuminemia but can denote the presence of a paraproteinemia or intoxication with lithium, bromide, or iodide. Elevated values most commonly indicate metabolic acidosis but can reflect laboratory error, metabolic alkalosis, hyperphosphatemia, or paraproteinemia. Metabolic acidosis can be divided into high anion and normal anion gap varieties, which can be present alone or concurrently. A presumed 1:1 stoichiometry between change in the serum anion gap (DeltaAG) and change in the serum bicarbonate concentration (DeltaHCO(3)(-)) has been used to uncover the concurrence of mixed metabolic acid-base disorders in patients with high anion gap acidosis. However, recent studies indicate variability in the DeltaAG/DeltaHCO(3)(-) in this disorder. This observation undercuts the ability to use this ratio alone to detect complex acid-base disorders, thus emphasizing the need to consider additional information to obtain the appropriate diagnosis. Despite these caveats, calculation of the serum anion gap remains an inexpensive and effective tool that aids detection of various acid-base disorders, hematologic malignancies, and intoxications.