The quickest and least expensive form of testing blood glucose (BG) is by point-of-care (POC) testing. However, critically ill patients have many coexisting conditions that raise the risk of an incorrect BG test result, and they may be taking therapeutics for those conditions that contribute to test inaccuracy too. This raises pretty big concerns, in particular because standard parameters of BG testing of critically ill patients have yet to be fully defined, and because current alternatives don’t fully address the concerns we have. Currently, hospital POC BG devices must meet the same standards as a device that’s used in the outpatient setting. According to the 2003 ISO 15197 standard, the parameters are BG <75 mg/dL, 95 percent of values within +15 mg/dL, and BG >75 mg/dL, 95 percent of values within +20 percent of the “reference” value (laboratory analyzed BG). However, the US Food and Drug Administration (FDA) is currently reviewing tighter BG parameters for allowable POC BG devices in the hospital, and in fact, an updated 2014 FDA draft recommendation is for a BG <70 mg/dL, 99 percent of values within +7 mg/dL of the reference range and the other 1 percent must not exceed +15 mg/dL. Also, for a BG >70 mg/dL, 99 percent of values within +10 percent of the “reference” value and the other 1 percent must not exceed +20 percent. The newer FDA parameters would permit a smaller glycemic range for different BG values, which would serve to enhance patient safety for BG readings. This is good news!
Other modalities for testing BG in the critical care setting do exist, and include arterial blood gas analyzers, Hemocue (for bedside hemoglobin testing), an i-STAT handheld blood analyzer, and laboratory tests of serum glucose. There are still concerns with these modalities though: cost of testing, sample volumes, accuracy, and turnaround time. And, generally, arterial blood demonstrates 5–10 mg/dL higher glucose levels compared with capillary and venous whole blood concentrations because of high glucose use in the extrahepatic tissues, mainly in the muscles.
Thankfully, the FDA is responding to these concerns and on January 7, 2014, it changed the labeling for all BG monitoring systems to include the following statement: “Performance of this system has not been evaluated on critically ill patients.” Similarly, in November, 2014, the Centers for Medicare and Medicaid Services (CMS) issued a warning in a Survey and Certification letter stating that use of a test outside of its intended FDA-approved/cleared use, limitations, or precautions, as indicated in the manufacturer’s instructions, would be considered off-label use and default the test to CLIA high-complexity. Then on March 13, 2015, the CMS stated in a draft memorandum, “In short, off-label use is not prohibited but does trigger the need for additional safeguards.” CMS also requested comments on the draft guidance.
In response to the FDA and CMS labeling change, the Medical University of South Carolina changed its policy. In order to comply with the FDA and CMS ruling, patients at MUSC who have anasarca, hypothermia (91.4 degrees Fahrenheit or 33 degrees Celsius), or hypotension requiring vasopressor support, need to have alternative means for BG testing other than capillary blood glucose (CBG) POC. Other routes for testing BG would be to obtain blood from the arterial line or venous site for POC BG (not CBG), use an i-STAT analyzer for BG, measure the arterial/venous glucose using a blood gas analyzer, or send the venous blood to the central lab for serum/plasma glucose. In our view, moving forward, it is important to approve the FDA 2014 draft recommendations. Indeed, it would be helpful for BG meter manufacturers to develop apparatus with improved accuracy. And, it would be beneficial to delay enforcement of the new standard for POC BG testing. Importantly, more studies are necessary to analyze which critically ill patients are at greatest risk of POC BG inaccuracy, and to determine which mode of testing is appropriate in select populations of patients.
In light of these developments, we have two key questions that we would like to present to readers:
- Should POC BG testing be allowed for use in critical illness?
- What alternative methodologies are available to measure glucose in patients who are critically ill?
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