vitamin C ascorbate can affect POC glucose

Administration of high doses of ascorbate (vitamin C), now employed either as a single agent or in combination with other medications in the treatment of severe burns and septic shock by many clinicians, is well described to give falsely elevated glucose levels when measurement is made by POCG bedside monitoring systems; the other medications listed have no such effect (choice A is correct; choices B, C, and D are incorrect). Other drugs that have been reported to interfere with POCG measurement include mannitol, acetaminophen, icodextrin (a peritoneal dialysate), and dopamine, although their effects are less predictable than high-dose ascorbate.

POCG systems carry the convenience of use of a small sample and a rapid turnaround time and are used to track the frequent fluctuations in serum glucose in critically ill patients. The rapid turnaround of the result is especially appealing when protocols are in place to treat the elevated glucose levels seen in many patients in the ICU. These bedside systems rely on electrochemical strips, and ascorbate, when given in large doses, can adhere to these strips, oxidize, and give artificially high glucose readings. Core laboratories (CLs) use spectrophotometric or calorimetric techniques to measure glucose levels, and these measurements are not confounded by circulating ascorbate. In one study of patients with burn shock receiving high-dose vitamin C infusions (66 mg/kg/h × 18 h), simultaneous blood samples were analyzed by POCG or CL methods. The mean POCG (225 ± 71 mg/dL [12.49 ± 3.94 mmol/L]) was significantly higher than the CL-determined levels (138 ± 30 mg/dL [7.66 ± 1.67 mmol/L]). No significant differences between the two methods were observed following discontinuation of the vitamin C infusions. Errors of this magnitude could have catastrophic effects in glucose management in critically ill patients with burns and septic shock, given their propensity for fluctuations in glucose levels and the existence of insulin treatment protocols in most ICUs. Accordingly, it is recommended that glucose monitoring be conducted by a CL during periods of vitamin C infusion in burn patients, in whom the highest infusion rates are often employed, and be considered as well for patients with septic shock receiving this medication.12345

Footnotes

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  2. Hager DN, Martin GS, Sevransky JE, et al. Glucometry when using vitamin C in sepsis: a note of caution. Chest. 2018;154(1):228-229. PubMed ↩

  3. Kahn SA, Lentz CW. Fictitious hyperglycemia: point-of-care glucose measurement is inaccurate during high-dose vitamin C infusion for burn shock resuscitation. J Burn Care Res. 2015;36(2):e67-e71. PubMed ↩

  4. Sartor Z, Kesey J, Dissanaike S. The effects of intravenous vitamin C on point-of-care glucose monitoring. J Burn Care Res. 2015;36(1):50-56. PubMed ↩

  5. Smith KE, Brown CS, Manning BM, et al. Accuracy of point-of-care blood glucose level measurements in critically ill patients with sepsis receiving high-dose intravenous vitamin C. Pharmacotherapy. 2018;38(11):1155-1161. PubMed ↩