Glucose Measurement in the ICU: Regulatory Intersects Reality*
Core to the management of dysglycemic patients, whether they have type 1 or type 2 diabetes (or one of its variants) or abnormal glucose homeostasis related to stress or associated pathology, is the need for timely and accurate glucose measurements. There are a number of challenges related to obtaining accurate glucose results in the ICU environment. Related to these challenges, the Food and Drug Administration (FDA) has recently issued a proposal calling for stricter application of glucose measurement standards in the critically ill (2) and has raised various questions about timeliness, cost, and realistic glucose analysis. Briefly, the FDA has proposed criteria for increased accuracy for prescription point-of-care (POC) glucose measurements for critically ill patients (“critically ill” has not been defined by the FDA) that are listed in Table 1. Please refer to recent review articles by Klonoff et al (3) and Rice and Coursin (4) for background regarding the specifics of the regulatory issues.
There is an abundance of literature regarding the inaccuracies surrounding ICU glucose measurements using POC meters (5–7). Two of these studies (6, 7) have even reported potential inaccurate dosing of insulin therapy and the resulting serious consequences from these erroneous measurements. Therefore, it is imperative that we trust our glucose meters and the methods they use to make these measurements in our critically ill patients.
A major issue with glucose measurement in this population is the sample site. Most ICU measurement, at least in the United States, is done with capillary blood (i.e., fingertip) (8), although arterial and venous blood samples are thought to be more accurate. Kuwa et al (9) reported the differences in glucose values from concurrently measured capillary, arterial, and venous blood samples. Also, Critchell et al (10) have reported similar findings, although it is unclear if the source of the inaccuracy may be the sample site, accuracy of the device itself, or both. Although the exact reason is unknown, it is generally believed that measurement of glucose from fingertip blood samples is not as accurate as more traditional blood sites (arterial or venous).
There is only one POC glucose meter currently approved for use in critically ill patients (Nova StatStrip; Nova Biomedical, Waltham, MA). In this issue of Critical Care Medicine (11), the manufacturer of this device has sponsored a multicenter trial that measured the accuracy and validity of glucose measurements across a wide spectrum of ICU patients. This five-center, international study compared venous and arterial blood glucose samples measured with a central laboratory device (CLD) to results for samples acquired simultaneously and measured using the POC Nova StatStrip meter (Nova Biomedical). They reported that this device yielded acceptable accuracy when compared with the CLD as measured by both the Clinical & Laboratory Standards Institute Point-of-Care Testing 12-A3 standards and when plotted on a Parkes error grid.
It is crucial to point out that all samples reported were obtained from either arterial or venous blood. Although capillary blood samples were obtained during the study, interestingly, the results and comparisons to CLD from these samples were not reported. It is important to note that this device is not approved for capillary blood measurement in the critically ill population.