Pseudohypobicarbonatemia

Introduction: Bicarbonate (HCO3) levels are measured by routine studies like Basic Metabolic Panel (BMP) or Blood Gases (BG). Generally, there is an acceptable level of correlation between the two tests. Rarely, there can be a discrepancy. Ours is one such case. Case Description: A 68 year old man was admitted to our facility on 6/24 with fatigue and poor oral intake for two weeks. The initial BMPwas notable for bicarbonate of 13 mmol/L and creatinine 4.9 mg/dL (Table 1). The initial BGresulted bicarbonate of 12. The bicarbonate levels obtained on 6/24 via BMP and BG co-related well. Subsequent multiple BMPs showed low bicarbonate levels and high anion gap even after resolution of the initial renal insult. The persistent hypobicarbonatemia on BMP triggered bicarbonate replacement. Blood gas on 7/11 showed HCO3 of 26 and BMP done on the same day showed HCO3 of 10 (Table 1). Our lab uses Dimension Vista (enzymatic method) for BMP; and on 8/3 we had our lab run the BMP by i-STAT CHEM8+ Cartridge (electrode method). The bicarbonate levels co-relatedwith the BG HCO3 (checked 7/31). On 8/20, we observed the same discrepancy on BMP – first sample was analyzed with enzymatic assay and the second sample utilized electrode method (Table 1). Simply, checking BMP via a different method helped explain the discrepancy. Discussion: Pseudohypobicarbonatemia implies falsely low bicarbonate levels. One must always explore the different laboratory testing techniques to account for the discrepancy. Bicarbonate levels as measured on Metabolic Panel and Blood Gas - Metabolic Panel Date 6/24 7/5 7/11 7/31 8/3 8/20 */^ Bicarbonate 13 12 10 12 27 10/22 Creatinine 4.9 1.0 0.8 0.8 0.7 0.7/0.7 Anion Gap 17 17 22 21 7 17/9 Blood Gas pH 7.23 7.47 7.42 Bicarbonate 12 26 24 1. Notice the discrepancy in bicarbonate levels on 7/11 (analysis done via Metabolic Panel and Blood Gas) 2. Also see the drastic difference in bicarbonate from Metabolic Panel (6/24 – 7/31) when enzymatic assay method was used and 8/3 when electrode method was used. 3. On 8/20 (asterisked/circumflexed) bicarbonate was checked on Metabolic Panel using enzymatic method first; and electrode method later; and there is notable difference in the two measurements.