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Anemia causes hypoglycemia in intensive care unit patients due to error in single-channel glucometers: Methods of reducing patient risk*

Pidcoke, Heather F. MD; Wade, Charles E. PhD; Mann, Elizabeth A. RN; Salinas, Jose PhD; Cohee, Brian M. BS; Holcomb, John B. MD; Wolf, Steven E. MD

doi: 10.1097/CCM.0b013e3181bc826f
Clinical Investigations

Objective: Intensive insulin therapy in the critically ill reduces mortality but carries the risk of increased hypoglycemia. Point-of-care blood glucose analysis is standard; however, anemia causes falsely high values and potentially masks hypoglycemia. Permissive anemia is practiced routinely in most intensive care units. We hypothesized that point-of-care glucometer error due to anemia is prevalent, can be corrected mathematically, and correction uncovers occult hypoglycemia during intensive insulin therapy.

Design: The study has both retrospective and prospective phases. We reviewed data to verify the presence of systematic error, determine the source of error, and establish the prevalence of anemia. We confirmed our findings by reproducing the error in an in vitro model. Prospective data were used to develop a correction formula validated by the Monte Carlo method. Correction was implemented in a burn intensive care unit and results were evaluated after 9 mos.

Setting: Burn and trauma intensive care units at a single research institution.

Patients/Subjects: Samples for in vitro studies were taken from healthy volunteers. Samples for formula development were from critically ill patients who received intensive insulin therapy.

Interventions: Insulin doses were calculated based on predicted serum glucose values from corrected point-of-care glucometer measurements.

Measurements and Main Results: Time-matched point-of-care glucose, laboratory glucose, and hematocrit values. We previously found that anemia (hematocrit <34%) produces systematic error in glucometer measurements. The error was correctible with a mathematical formula developed and validated, using prospectively collected data. Error of uncorrected point-of-care glucose ranged from 19% to 29% (p < .001), improving to ≤5% after mathematical correction of prospective data. Comparison of data pairs before and after correction formula implementation demonstrated a 78% decrease in the prevalence of hypoglycemia in critically ill and anemic patients treated with insulin and tight glucose control (p < .001).

Conclusions: A mathematical formula that corrects erroneous point-of-care glucose values due to anemia in intensive care unit patients reduces the prevalence of hypoglycemia during intensive insulin therapy.

From the United States Army Institute of Surgical Research (HFP, CEW, EAM, JS, BMC, JBH, SEW), Fort Sam Houston, TX; and the Department of Surgery (HFP, CEW, JBH, SEW), University of Texas Health Science Center - San Antonio, San Antonio, TX.

Supported, in part, by Grant 1 R01 GM063120-04 from the National Institutes of Health (NIH) and The Technologies for Metabolic Monitoring/Julia Weaver Fund, a Congressionally Directed Program Jointly Managed by the US Army Medical Research and Materiel Command, NIH, NASA, and the Juvenile Diabetes Research Foundation and Combat Casualty Care Division United States Army Medical Research and Materiel Command.

The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Department of Defense or United States Government. The authors are affiliated with or employed by the U.S. government. This work was prepared as part of their official duties and, as such, there is no copyright to be transferred.

The authors have not disclosed any potential conflicts of interest.

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© 2010 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins