ISSN: 2642-6145
Authors: Max Brock, Shuling Fan and Steven C Borkan*
Accurate bicarbonate measurement is critical for assessing acid-base status. This study characterizes the cause of an unexpected discrepancy between a common bicarbonate assay and the bicarbonate calculated from blood gasses in nine cases identified at a single medical center over a 12-month observation period. Hospitalized patients with at least a 3 mEq/L difference between the plasma bicarbonate measured by a photometric assay and a blood gas were investigated to determine the cause. All patients experienced a fall in measured bicarbonate associated in clinical scenarios in which progressive metabolic acidosis was suspected. Electrolyte, acid-base status, triglyceride, turbidity index and clinical histories were obtained in all patients. The mean bicarbonate discrepancy was >8 mEq/L (range 3.4-12 mEq/L). All patients (9/9) experienced transient hyperlipidemia that persisted as the lipid level fell below that typically detected by a turbidity index and was not matched by a fall in pH or the calculated bicarbonate level. The effect of lipid addition and removal on measured bicarbonate was investigated to replicate or minimize the detected bicarbonate discrepancy, respectively. A positive correlation between the severity of the bicarbonate discrepancy measured by a common photometric assay and hyperlipidemia occurred. This discrepancy persisted below the lipid level detected by a visual turbidity index, was not matched by a fall in pH or the calculated bicarbonate level. Lipid interference is distinct from the dilutional mechanism of pseudohyponatremia and is independent of the specific autoanalyzer, operator, and institution. Pseudohypobicarbonatemia increased resource utilization in the absence of clinical deterioration or supporting laboratory data to suggest progressive metabolic acidosis. At high levels, the addition of exogenous lipid replicated the bicarbonate discrepancy. We show that pseudohypobicarbonatemia is associated with transient hyperlipidemia. Lipid removal from blood samples prior to biochemical assay combined with increased clinical awareness of this phenomenon minimizes the untoward impact of this phenomenon resource utilization and clinical practice.
Keywords: Pseudometabolic Acidosis; Hypertriglyceridemia; Hyperlipidemia; Chromatogenic Interfering Substance; Pseudohypobicarbonatemia; Pseudohyponatremia
