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Devices, decisions: POC glucose in the critically ill

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Anne Ford

January 2018—Using point-of-care glucose meters in critically ill patients can feel like tiptoeing through a regulatory minefield. Perhaps your preferred meter hasn’t been cleared by the FDA for use in this population. Or maybe you’re not sure which assay performance requirements should be regulating the performance of your meters. Or perhaps you’re still trying to define “critically ill.”

Recently published studies have aimed to clear some of those mines by evaluating the accuracy of glucose meter results in ICU and non-ICU settings and by also assessing meter performance in a clinical context rather than a strictly analytical manner.

Those studies, the four options labs have, and a look at the POC policy in place at Ohio State University Wexner Medical Center were spotlighted at last year’s AACC annual meeting in a session, “The Burden of Proof for Point-of-Care Glucose Monitoring in Critically Ill Patients,” presented by James H. Nichols, PhD; Alison Woodworth, PhD; and Steven Cotten, PhD.

While nursing tends to think that capillary samples are easier than phlebotomy, Dr. Nichols said, variations in operator technique mean there is ample room for error. And getting an adequate reflection of the patient’s physiology isn’t a given. What if the patient is cold and the fingertips are blue, is in shock, or has peripheral vascular disease and the fingertip isn’t perfused well? “You’re not going to get an adequate reflection of what’s going on in terms of physiology,” Dr. Nichols said. “And this is where the FDA’s concern has been for use of glucose meters on these specific types of patients.”

Roche’s Accu-Chek Inform II is used at Vanderbilt University School of Medicine, where Dr. Nichols is professor of pathology, microbiology, and immunology and medical director of clinical chemistry and point-of-care testing. Among the limitations of the device, Dr. Nichols said: “If peripheral circulation is impaired, collection of capillary blood from approved sample sites is not advised as the results might not be a true reflection of the physiologic blood glucose level that’s more central in that patient.” That may apply in circumstances of severe dehydration as a result of diabetic ketoacidosis or due to hyperosmolar hyperglycemic non-ketotic syndrome, hypotension, shock, decompensated heart failure, or peripheral arterial occlusive disease.

Another limitation, and this is what “has been forced by the FDA on all glucose meter manufacturers,” Dr. Nichols said, is that the performance of the system has not been evaluated in the critically ill. “So what does that exactly mean? Who are the critically ill? Are they just the people in our ICUs or are they elsewhere in our health system?” Each institution must define that term for itself.

When blood glucose monitoring system manufacturer instructions contain such a limitation, the use of that system on critically ill patients is considered off-label. That means, of course, it will automatically default to high complexity under CLIA—“with all the ramifications that has in terms of education of staff who can perform the testing and the documentation, the validation of the method, and the ongoing proficiency and documentation that’s required,” Dr. Nichols noted.

In response, experts from industry, government, and academia created a white paper, “POCT17: Use of Glucose Meters for Critically Ill Patients,” released in 2016 by the Clinical and Laboratory Standards Institute. Dr. Nichols, chairholder, outlined the four options the paper presents for laboratories.

Option one: Follow the manufacturer’s instructions, as Dr. Nichols and his team do at Vanderbilt. “We have already taught our staff to not use those meters on patients who have these limitations,” he said. “So we’re really not changing practice. We simply said: For our institution, we’re defining ‘critically ill’ as any of the limitations in the manufacturer’s package insert.” This option is least disruptive for the staff, he said, “and it meets the letter of the regulatory law.”

Dr. Nichols

Dr. Nichols

A poll of audience members found that 37 percent of those responding are following manufacturer limitations and, in those cases, using alternative sample types, such as venous and arterial draws instead of capillary. (The second most popular option among the audience, at 18 percent: allowing capillary samples as clinicians deem necessary.)

Option two: Switch to a meter that is cleared for use in critically ill patients. Nova Biomedical’s StatStrip has such clearance but only for venous, arterial, and neonatal arterial and heel stick whole blood specimens. About 16 percent of audience members indicated they had chosen this route. “Even for that meter,” Dr. Nichols emphasized, “you cannot use capillary samples” for the critically ill.

Option three: Stop using glucose meters in all critically ill patients, and instead use an alternative method such as a blood gas analyzer or send the sample to the laboratory, as about 13 percent of the audience is doing.

Option four: Use the glucose meter off-label, meaning that, as Dr. Nichols said, “you revert to CLIA high complexity, you have to do validation in critically ill patients, and you are also now limited, based on your state and based on CLIA regulations, in who can actually perform testing.” About 16 percent of the audience reported using this approach.

Dr. Nichols warns labs about indirect phlebotomy, or line draws. “Many of our critically ill patients are not going to have venous or arterial samples collected individually on them,” he said. “They have indwelling lines, and their samples are going to be collected off these indwelling catheters, and that’s an issue because of the potential to contaminate the sample with whatever is in that line.” Depending on the test, it can dilute or even elevate the results. “If you collect through a heparin lock, think about coagulation testing and use of PT or PT INRs after you have collected through that line—they will be impacted.” Use of an IV line is not generally recommended, he noted, “but yet it tends to be universal practice. So be aware of that limitation.”

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