Kidney Week

Abstract: TH-PO0418

When Numbers Don't Add Up: A Rare Case of Pseudohypobicarbonatemia in Severe Hypertriglyceridemia

Session Information

• Fluid, Electrolyte, and Acid-Base Disorders: Clinical - 1
  November 06, 2025 | Location: Exhibit Hall, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Fluid, Electrolytes, and Acid-Base Disorders

• 1102 Fluid, Electrolyte, and Acid-Base Disorders: Clinical

Authors

• Ekiz, Esra, Trinity Health of New England, Hartford, Connecticut, United States

Esra Ekiz, MD

• Ayafor, Vanessa, Trinity Health of New England, Hartford, Connecticut, United States

Vanessa Ayafor, MD

• Zhang, He, Trinity Health of New England, Hartford, Connecticut, United States

He Zhang, MD, PhD

• Rho, Mira, Trinity Health of New England, Hartford, Connecticut, United States

Mira Rho, MD, FASN

Introduction

Serum bicarbonate is typically assessed via automated chemistry analyzers measuring total CO₂ or arterial/venous blood gas (A/VBG) analysis using the Henderson-Hasselbalch equation. While these methods usually align, discrepancies can occur due to assay interference. Pseudohyponatremia from hyperlipidemia is well known; however, pseudohypobicarbonatemia remains underrecognized. We present a case highlighting this rare phenomenon caused by severe hypertriglyceridemia.

Case Description

A 46-year-old woman with a history of GERD, umbilical hernia, iron deficiency anemia, and prediabetes presented with acute-on-chronic periumbilical abdominal pain. She denied nausea, vomiting, or diarrhea. Physical exam revealed mild umbilical tenderness without peritoneal signs.

Initial labs showed hemoglobin 9.2 g/dL, hematocrit 29%, MCV 71.3 fL, glucose 274 mg/dL, and HbA1c 9.7%. Serum bicarbonate was <10 mmol/L with an anion gap >19. However, VBG showed a pH of 7.37, pCO₂ 45 mmHg, and bicarbonate 24.8 mmol/L. Urine drug screen and toxic alcohol panel were negative; abdominal imaging was unremarkable.

A lipid panel revealed triglycerides of 2,390 mg/dL. The patient was started on IV insulin, leading to a reduction in triglycerides to <500 mg/dL and normalization of serum bicarbonate to 24 mmol/L.

Discussion

Pseudohypobicarbonatemia, first described in 2010s, remains rare with approximately a dozen reported cases ¹. While the exact mechanism is not fully understood, theories suggest interference in enzymatic or spectrophotometric assays by lipemic samples. The Siemens Atellica system used in our lab relies on an enzymatic method involving NADH oxidation detected at 410/478 nm ². Hyperlipidemia, through its space-occupying and light-scattering effects ³, may reduce the accuracy of bicarbonate measurement in such systems. Notably, our patient did not exhibit pseudohyponatremia despite severe hypertriglyceridemia, suggesting that spectrophotometric interference may play a more significant role than simple aqueous displacement in bicarbonate measurement ⁴.

This case emphasizes the importance of correlating lab values with clinical context and ABG findings. Awareness of pseudohypobicarbonatemia is essential to avoid misdiagnosis and unnecessary interventions. Clinicians should remain mindful of laboratory assay limitations, particularly in patients with marked hyperlipidemia

Digital Object Identifier (DOI)

• doi: 10.1681/ASN.2025ps6r3cj8