Abstract: SA-PO1016

Total CO2 Assay Interference Induced by Hypertriglyceridemia

Session Information

Category: Nephrology Education

  • 1302 Fellows and Residents Case Reports

Authors

  • Beltran Melgarejo, Diego Andres, Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Bhave, Gautam B., Vanderbilt University Medical Center, Nashville, Tennessee, United States
  • Burgner, Anna Marie, Vanderbilt University Medical Center, Nashville, Tennessee, United States
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.