How accurately do we measure blood glucose levels in intensive care unit (ICU) patients?

The extended internal QC (eIQC): a new practical approach for quality assurance in point-of-care glucose testing using the POCTopus Software – a pilot study

Background

Quality assurance (QA) in point-of-care testing (POCT) is an important issue for organizing POCT structures within the healthcare sector. In Germany, only one device needs to participate in an external QA program, if the responsible core laboratory is supervising internal quality controls of all other identical POCT devices. This flexible definition of quality control (QC) testing is in line with the fundamentals of ISO 22870 and the ISO 15189, but can only be regarded as a minimum requirement.

Methods

We present a pilot study for an inexpensive new approach for additional POCT QC measurement similar to the external QA program within the medical laboratory using capillary glucose measurement as an example. This new system, referred to as “extended internal QC (eIQC)”, uses in-house generated QC material from leftover full blood from routine diagnostics. We provide information on calculation of target values and acceptance ranges and preliminary data on stability and comparison between POCT and core laboratory testing (COBAS 8000). Additionally, we simulated the approach using three devices within the laboratory as surrogate for three POCT sites. In this pilot study, measurements of QC material beyond the mandatory QA plan are structured and optimized through the use of the POCTopus Software solution.

Results

QC material was easily generated including specification of target values. The software aided in automatized processing of the samples. The software showed limitations in evaluation and monitoring without relevant use of resources. We found a significant bias between measurements on POCT and COBAS 8000 instruments.

Conclusions

The presented new approach for additional QAs for POCT enables POCT coordinators to establish an additional safety and QC level. Further software improvements are required. Further studies are needed for validation and comparison measurements between methods. Overall, this approach offers great potential for POCT structures seeking higher quality standards.

Clinical Reliability of Point-of-Care Glucose Testing in Critically Ill Patients

BACKGROUND

Point-of-care (POC) glucometers are commonly used in intensive care units (ICUs). The Centers for Medicare & Medicaid Services have called into question the accuracy of POC glucometers in critically ill patients. This study sought to identify specific characteristics within our facility's ICU patients that were associated with inaccuracies in POC glucose measurements.

METHODS

We conducted a prospective cohort study that compared POC capillary blood glucose samples with venous samples collected in our ICU. All nonpregnant patients >18 years old admitted to the ICU with orders for daily laboratory testing that included blood glucose were eligible for inclusion.

RESULTS

A total of 46 patients were enrolled and 85 samples were collected. The mean difference between venous and POC samples was 5.23 mg/dL (95% CI, 3.16-7.3 mg/dL). Measurement inaccuracies would have altered treatment in 7/85 instances (8.2%). The only clinically significant inaccuracy found was the omission of 2 units of insulin in 1 hyperglycemic patient. Measurement inconsistencies generally underestimated low blood glucose values (2/2 instances) and overestimated high blood glucose values (4/5 instances).

CONCLUSIONS

In our study, the mean difference between venous and POC glucose samples was small. Similarly, measurement inaccuracies that would have altered treatment were rare and only one instance was deemed clinically significant. We conclude that POC capillary glucose testing within our cohort and in similar critically ill patients is likely safe and effective.

Performance of strip-based glucose meters and cassette-based blood gas analyzer for monitoring glucose levels in a surgical intensive care setting

BACKGROUND

We verified the analytical performance of strip-based handheld glucose meters (GM) for prescription use, in a comparative split-sample protocol using blood gas samples from a surgical intensive care unit (ICU).

METHODS

Freestyle Precision Pro (Abbott), StatStrip Connectivity Meter (Nova), ACCU-CHEK Inform II (Roche) were evaluated for recovery/linearity, imprecision/repeatability. The GMs and the ABL90 (Radiometer) blood gas analyzer (BGA) were tested for relative accuracy vs. the comparator hexokinase glucose-6-phosphate-dehydrogenase (HK/G6PDH) assay on a Cobas c702 analyzer (Roche).

RESULTS

Recovery of spiked glucose was linear up to 19.3 mmol/L (347 mg/dL) with a slope of 0.91-0.94 for all GMs. Repeatability estimated by pooling duplicate measurements on samples below (n=9), in (n=51) or above (n=80) the 4.2-5.9 mM (74-106 mg/dL) range were for Freestyle Precision Pro: 4.2%, 4.0%, 3.6%; StatStrip Connectivity Meter: 4.0%, 4.3%, 4.5%; and ACCU-CHEK Inform II: 1.4%, 2.5%, 3.5%. GMs were in agreement with the comparator method. The BGA outperformed the GMs, with a MARD of 3.9% compared to 6.5%, 5.8% and 4.4% for the FreeStyle, StatStrip and ACCU-CHEK, respectively. Zero % of the BGA results deviated more than the FDA 10% criterion as compared to 9.4%, 3.7% and 2.2% for the FreeStyle, StatStrip and ACCU-CHEK, respectively. For all GMs, icodextrin did not interfere. Variation in the putative influence factors hematocrit and O2 tension could not explain observed differences with the comparator method.

CONCLUSIONS

GMs quantified blood glucose in whole blood at about the 10% total error criterion, proposed by the FDA for prescription use.

Critical Care Glucose Point-of-Care Testing

Maintaining blood glucose concentration within an acceptable range is a goal for patients with diabetes mellitus. Point-of-care glucose meters initially designed for home self-monitoring in patients with diabetes have been widely used in the hospital settings because of ease of use and quick reporting of blood glucose information. They are not only utilized for the general inpatient population but also for critically ill patients. Many factors affect the accuracy of point-of-care glucose testing, particularly in critical care settings. Inaccurate blood glucose information can result in unsafe insulin delivery which causes poor glucose control and can be fatal. Healthcare professionals should be aware of the limitations of point-of-care glucose testing. This chapter will first introduce glucose regulation in diabetes mellitus, hyperglycemia/hypoglycemia in the intensive care unit, importance of glucose control in critical care patients, and pathophysiological variables of critically ill patients that affect the accuracy of point-of-care glucose testing. Then, we will discuss currently available point-of-care glucose meters and preanalytical, analytical, and postanalytical sources of variation and error in point-of-care glucose testing.

Challenges of inpatient blood glucose monitoring: standards, methods, and devices to measure blood glucose

Glucose control in the hospital setting is very important. There is a high incidence of hyperglycemia, hypoglycemia, and glycemic variability in hospitalized patients. Safe insulin delivery and glucose control is dependent on reliable glucose meters and monitoring systems in the hospital. Different glucose monitoring systems use arterial, venous, central venous, and capillary blood samples. It is important for clinicians to be aware that there are limitations of specific point-of-care (POC) glucose meters and that situations exist whereby POC glucose meters as the sole measurement device should be avoided. POC meter devices are not approved by the Food and Drug Administration for use in critical care, although POC meter devices are commonly used in critical care settings and elsewhere. This review focuses on glucose assay principles, instrument technology, influences on glucose measurement, standards for glucose measurement, and an evaluation of different methods to measure blood glucose in the hospital setting.

Point-of-care blood glucose testing for diabetes care in hospitalized patients: an evidence-based review

Glycemic control in hospitalized patients with diabetes requires accurate near-patient glucose monitoring systems. In the past decade, point-of-care blood glucose monitoring devices have become the mainstay of near-patient glucose monitoring in hospitals across the world. In this article, we focus on its history, accuracy, clinical use, and cost-effectiveness. Point-of-care devices have evolved from 1.2 kg instruments with no informatics to handheld lightweight portable devices with advanced connectivity features. Their accuracy however remains a subject of debate, and new standards for their approval have now been issued by both the International Organization for Standardization and the Clinical and Laboratory Standards Institute. While their cost-effectiveness remains to be proved, their clinical value for managing inpatients with diabetes remains unchallenged. This evidence-based review provides an overall view of its use in the hospital setting.

Comparative Accuracy of 3 Blood Glucose Monitoring Systems that Communicate with an Insulin Pump

OBJECTIVE

This study compared the accuracy of the Contour® Next Link blood glucose monitoring system (BGMS) with 2 other BGMSs (OneTouch® UltraLink® and Nova Max Link™), all 3 of which can communicate wirelessly with an insulin pump.

METHODS

Study staff tested fingerstick samples from 112 subjects aged ≥18 years with each BGMS. All BGMS results were compared to YSI 2300 STAT Plus™ Glucose Analyzer results from the same sample source. To safely obtain a wide range of glucose values, 3 blood samples were obtained from each subject (1 sample was tested fresh from the fingertip [unmodified], and the other 2 samples were modified to raise or lower the glucose concentration). The primary endpoint evaluated was difference in accuracy among the BGMSs across the entire tested glucose range (34 to 561 mg/dL). Additional comparisons were made of accuracy in the low (≤80 mg/dL) and high (>180 mg/dL) glucose ranges. BGMS accuracy was assessed by mean absolute relative difference (MARD).

RESULTS

The Contour® Next Link BGMS had a statistically significantly lower MARD from the reference value than the other BGMSs across the entire tested glucose range, calculated using all samples as well as only unmodified (i.e., natural) samples. In the low and high glucose ranges, the Contour® Next Link also had a statistically significantly lower MARD from the reference value than the other BGMSs.

CONCLUSION

As assessed by MARD, the Contour® Next Link BGMS was significantly more accurate than the other BGMSs evaluated, all of which can communicate wirelessly with an insulin pump.

Performance of cassette-based blood gas analyzers to monitor blood glucose and lactate levels in a surgical intensive care setting

BACKGROUND

With the use of a traditional blood gas analyzer (BGA) (ABL800 Radiometer) for blood glucose monitoring, tight glucose control (TGC) reduced in-hospital mortality and morbidity of surgical intensive care unit (ICU) adult and pediatric patients. Such BGAs are now superseded by cassette-based BGAs. We assessed the analytical reliability of cassette-based BGAs to monitor patient's metabolic status in an ICU setting.

METHODS

We evaluated recovery/linearity, imprecision/repeatability and relative accuracy vs. comparison methods for glucose [coupled hexokinase glucose-6-phosphate dehydrogenase (HK/G6PD) assay] and lactate (lactate dehydrogenase assay) in ICU patient samples with two cassette-based BGAs [RP500 (Siemens) and ABL90 (Radiometer)] and with the ABL800 BGA.

RESULTS

Recovery of spiked glucose up to 348 mg/dL (19.3 mmol/L) was complete for all BGAs. Repeatability of ABL800 and ABL90 was comparable with the comparison method (about 1%), but higher for RP500 (about 2.4%). All BGAs were in agreement with the comparison method, with all glucose measurements falling within preset 10% criteria suggested by Karon. Recovery of spiked lactate (up to 25 mmol/L) was incomplete at all levels. Repeatability of ABL800 and ABL90 was comparable with the comparison method (about 4%), and 5.5% for RP500. All BGAs were in agreement with the comparison method, with >98% of the lactate measurements falling within 30% biological-variation-based criteria.

CONCLUSIONS

The cassette-based BGAs quantified blood glucose and lactate levels in ICU patients within the acceptable error ranges. Cassette-based BGAs can be used for monitoring patient's metabolic status in an ICU setting.

Spontaneous subarachnoid hemorrhage and glucose management

Although metabolic abnormalities have been linked with poor outcome after subarachnoid hemorrhage, there are limited data addressing the impact of glycemic control or benefits of glucose management after aneurysmal subarachnoid hemorrhage. A systematic literature search was conducted of English-language articles describing original research on glycemic control in patients with subarachnoid hemorrhage. Case reports and case series were excluded. A total of 22 publications were selected for this review. Among the 17 studies investigating glucose as an outcome predictor, glucose levels during hospitalization were more likely to predict outcome than admission glucose. In general, hyperglycemia was linked to worse outcome. While insulin therapy in subarachnoid hemorrhage patients was shown to effectively control plasma glucose levels, plasma glucose control was not necessarily reflective of cerebral glucose such that very tight glucose control may lead to neuroglycopenia. Furthermore, tight glycemic control was associated with an increased risk for hypoglycemia which was linked to worse outcome.

Blood glucose measurements in critically ill patients

Studies on tight glycemic control by intensive insulin therapy abruptly changed the climate of limited interest in the problem of hyperglycemia in critically ill patients and reopened the discussion on accuracy and reliability of glucose sensor devices. This article describes important components of blood glucose measurements and their interferences with the focus on the intensive care unit setting. Typical methodologies, organized from analytical accuracy to clinical accuracy, to assess imprecision and bias of a glucose sensor are also discussed. Finally, a list of recommendations and requirements to be considered when evaluating (time-discrete) glucose sensor devices is given.

Glucose management in the neurosurgical patient: are we yet any closer?

PURPOSE OF REVIEW

This review focuses on recent findings in perioperative management of blood glucose control using intensive insulin therapy in neurosurgical and neurocritical care and in other intensive care unit patients. We also aim to address practical issues and make recommendations that may contribute to the safe clinical application of intensive insulin therapy targeted to optimize blood glucose control in these patients.

RECENT FINDINGS

Intensive insulin therapy targeted to obtain tight blood glucose control induces a substantial increase in the number of hypoglycemic episodes and mortality rate. On the contrary, hyperglycemia--both isolated episodes and high mean glucose levels--is associated with worsened neurologic outcome and increased mortality.

SUMMARY

In neurosurgical and neurocritical care as well as other intensive care unit patients, both hypoglycemia and hyperglycemia have significant adverse effects. The optimal glucose level remains under debate but significant steps have evolved with the call for judicious control and elimination of the historical approach to glycemic management, which underestimated drawbacks associated with dysglycemia. The increased incidence of hypoglycemia and mortality as well as the impact of hyperglycemia on worsening neurologic function in patients with acute brain damage heightens the need for more clinical studies on perioperative glucose management in these patients.

Increased hypoglycemia associated with renal failure during continuous intravenous insulin infusion and specialized nutritional support

OBJECTIVE

To evaluate glycemic control for critically ill, hyperglycemic trauma patients with renal failure who received concurrent intensive insulin therapy and continuous enteral nutrition (EN) or parenteral nutrition (PN).

METHODS

Adult trauma patients with renal failure who were given EN or PN concurrently with continuous graduated intravenous regular human insulin (RHI) infusion for at least 3 d were evaluated. Our conventional RHI algorithm was modified for those with renal failure by allowing greater changes in blood glucose (BG) concentrations before the infusion rate was escalated. BG concentration was determined every 1 to 2 h while receiving the insulin infusion. BG control was evaluated on the day before RHI infusion and for a maximum of 7 d while receiving RHI. Target BG during the RHI infusion was 70 to 149 mg/dL (3.9 to 8.3 mmol/L). Glycemic control and incidence of hypoglycemia for those with renal failure were compared with a historical cohort of critically ill, hyperglycemic trauma patients without renal failure given our conventional RHI algorithm.

RESULTS

Twenty-one patients with renal failure who received the modified RHI algorithm were evaluated and compared with 40 patients without renal failure given our conventional RHI algorithm. Average BG concentration was significantly greater for those with renal failure (133±14 mg/dL or 7.3±0.7 mmol/L) compared with those without renal failure (122±15 mg/dL or 6.8±0.8 mmol/L), respectively (P<0.01). Patients with renal failure showed worsened glycemic variability, with 16.1±3.3 h/d within the target BG range, 6.9±3.2 h/d above the target BG range, and 1.4±1.1 h/d below the target BG range compared with 19.6±4.7 h/d (P<0.001), 3.4±3.0 h/d (P<0.001), and 0.7±0.8 h/d (P<0.01) for those without renal failure, respectively. Moderate hypoglycemia (<60 mg/dL or<3.3 mmol/L) occurred in 76% of patients with renal failure compared with 35% without renal failure (P<0.005). Severe hypoglycemia (BG<40 mg/dL or<2.2 mmol/L) occurred in 29% of patients with renal failure compared with none of those without renal failure (P<0.001).

CONCLUSION

Despite receiving a modified RHI infusion, critically ill trauma patients with renal failure are at greater risk for developing hypoglycemia and have more glycemic variability than patients without renal failure.

The food and drug administration is now preparing to establish tighter performance requirements for blood glucose monitors

On March 16 and 17, 2010, the Food and Drug Administration (FDA) presented a public meeting about blood glucose monitoring at the Gaithersberg Hilton Hotel. The meeting was intended to present expert opinions and solicit input from the public about whether to develop new regulatory policies for blood glucose monitors. The meeting was divided into three sections: (1) Clinical Accuracy Requirements for Blood Glucose Monitors, (2) Interferences and Limitations of Blood Glucose Monitors, and (3) Tight Glycemic Control. Many officials from the Center for Devices and Radiologic Health and the Office of In Vitro Diagnostic Devices, which are the parts of FDA that regulate approval of blood glucose monitors, either spoke on the agenda or attended in the audience. Approximately 300 people attended; they were mostly clinicians (such as adult endocrinologists, pediatric endocrinologists, internists, clinical chemists, intensivists, surgeons, nurses, and diabetes educators) or industry officials from companies involved in glucose monitoring, pharmaceutical products, data analysis, or regulatory consulting.