Kidney Week

Abstract: SA-PO1016

Total CO2 Assay Interference Induced by Hypertriglyceridemia

Session Information

• Fellows/Residents Case Reports: Fluid, Electrolytes, Acid Base
  November 04, 2017 | Location: Hall H, Morial Convention Center
  Abstract Time: 10:00 AM - 10:00 AM

Category: Nephrology Education

• 1302 Fellows and Residents Case Reports

Authors

• Beltran Melgarejo, Diego Andres, Vanderbilt University Medical Center, Nashville, Tennessee, United States

Diego Andres Beltran Melgarejo,

• Bhave, Gautam B., Vanderbilt University Medical Center, Nashville, Tennessee, United States

Gautam B. Bhave,

• Burgner, Anna Marie, Vanderbilt University Medical Center, Nashville, Tennessee, United States

Anna Marie Burgner,

Background

Measurement of CO₂ is a key component of acid base assessment. Although modern laboratory instruments provide high accuracy and reliability, assays are still prone to error. We present a case where interference in CO₂ measurement lead to significant disparities between total CO₂, calculated CO₂, and clinical findings.

Methods

A 55-year-old female with type 1 diabetes mellitus and alcohol abuse, presented with 1 day of dyspnea, palpitations, vomiting and abdominal pain. She reported recent binge drinking, poor dietary intake and missing insulin doses. Physical exam revealed sinus tachycardia and no other abnormalities.
Workup indicated acute liver failure, anuric acute kidney failure, and a high anion gap metabolic acidosis initially attributed to ketoacidosis. There was a discordance on labs with total CO₂ (TCO₂) measuring 13mmol/L and venous blood gases (VBG) showing a pH of 7.33 , pCO₂ of 33 mmHg, and calculated HCO₃ (cHCO₃) 17mmol/L. On follow up labs, tCO₂ dropped to <5 mmol/L, while VBG continued to show pH>7.33, and cHCO3 >18mmol/L. Discrepancies amongst tCO₂, cHCO₃, and clinical findings suggested a falsely low tCO₂ result. There was no hemolysis or significant hyperbilirubinemia, which commonly interfere with the tCO₂ assay, however triglycerides (TG) were 1712mg/dL, and the serum sample was markedly lipemic on visual inspection.
She was treated with normal saline, insulin drip, and continuous renal replacement therapy. The discrepancy between tCO₂ and cHCO₂ resolved as TG improved. Hepatic and renal failure resolved.

Conclusion

Measurement of tCO₂ can be achieved by electrode-based assay or as in this case by spectrophotometry. Lipemia might interfere with the latter, as large lipid particles like VLDL and chylomicrons absorb or disperse light, leading to erroneous results. Although manufacturers report minimal error with TG of 1000-2000mg/dL, this error is estimated using a lipid emulsion (Intralipid) that does not match the large size of TG particles. Mixing experiments by Wiencek et al, demonstrated a greater negative CO₂ error when estimates are based on TG dilutions instead of Intralipid testing. This case illustrates that accurate acid base assessment requires a careful clinical interpretation of tCO₂/cHCO₃ and patient’s clinical condition.