Gerald J. Kost

Effects of Different Hematocrit Levels on Glucose Measurements With Handheld Meters for Point-of-Care Testing

OBJECTIVES To determine the effects of low, normal, and high hematocrit levels on glucose meter measurements and to assess the clinical risks of hematocrit errors. DESIGN Changes in glucose measurements between low and high hematocrit levels were calculated to determine hematocrit effects. The differences between glucose measured with meters and with a plasma glucose method (YSI 2300) also were compared. SETTING Six hand-held glucose meters were assessed in vitro at low (19.1%), normal (38.5%), and high (58.3%) hematocrit levels, and at 6 glucose concentrations ranging from 2.06 mmol/L (37.1 mg/dL) to 30.24 mmol/L (544.7 mg/dL). RESULTS Most systems, regardless of the reference to which they were calibrated, demonstrated positive bias at lower hematocrit levels and negative bias at higher hematocrit levels. Low, normal, and high hematocrit levels progressively lowered Precision G and Precision QID glucose measurements. Hematocrit effects on the other systems were more dependent on the glucose concentration. Overall, Accu-Chek Comfort Curve showed the least sensitivity to hematocrit changes, except at the lowest glucose concentration. CONCLUSIONS We strongly recommend that clinical professionals choose glucose systems carefully and interpret glucose measurements with extreme caution when the patients hematocrit value changes, particularly if there is a simultaneous change in glucose level.

Point-of-Care Glucose Testing Effects of Critical Care Variables, Influence of Reference Instruments, and a Modular Glucose Meter Design

OBJECTIVE To assess the clinical performance of glucose meter systems when used with critically ill patients. DESIGN Two glucose meter systems (SureStepPro and Precision G) and a modular adaptation (Immediate Response Mobile Analysis-SureStepPro) were assessed clinically using arterial samples from critically ill patients. A biosensor-based analyzer (YSI 2700) and a hospital chemistry analyzer (Synchron CX-7) were the primary and secondary reference instruments, respectively. PATIENTS AND SETTING Two hundred forty-seven critical care patients at the University of California, Davis, Medical Center participated in this study. OUTCOME MEASURES Error tolerances of +/-15 mg/dL for glucose levels </=100 mg/dL and +/-15% for glucose levels >100 mg/dL were used to evaluate glucose meter performance; 95% of glucose meter measurements should fall within these tolerances. RESULTS Compared to the primary reference method, 98% to 100% of SureStepPro and 91% to 95% of Precision G measurements fell within the error tolerances. Paired differences of glucose measurements versus critical care variables (Po(2), pH, Pco(2), and hematocrit) were analyzed to determine the effects of these variables on meter measurements. Po(2) and Pco(2) decreased Precision G and SureStepPro measurements, respectively, but not enough to be clinically significant based on the error tolerance criteria. Hematocrit levels affected glucose measurements on both meter systems. Modular adaptation did not affect test strip performance. CONCLUSIONS Glucose meter measurements correlated best with primary reference instrument measurements. Overall, both glucose meter systems showed acceptable performance for point-of-care testing. However, the effects of some critical care variables, especially low and high hematocrit values, could cause overestimated or underestimated glucose measurements.

Effects of Drugs on Glucose Measurements With Handheld Glucose Meters and a Portable Glucose Analyzer

Thirty drugs used primarily in critical care and hospital settings were tested in vitro to observe interference on glucose measurements with 6 hand-held glucose meters and a portable glucose analyzer. Paired differences of glucose measurements between drug-spiked samples and unspiked control samples were calculated to determine bias. A criterion of +/- 6 mg/dL was used as the cutoff for interference. Ascorbic acid interfered with the measurements on all glucose devices evaluated. Acetaminophen, dopamine, and mannitol interfered with glucose measurements on some devices. Dose-response relationships help assessment of drug interference in clinical use. High dosages of these drugs may be given to critically ill patients or self-administered by patients without medical supervision. Package inserts for the glucose devices may not provide adequate warning information. Hence, we recommend that clinicians choose glucose devices carefully and interpret results cautiously when glucose measurements are performed during or after drug interventions.

Oxygen effects on glucose meter measurements with glucose dehydrogenase- and oxidase-based test strips for point-of-care testing

ObjectivesTo determine the effects of different oxygen tensions (Po2) on glucose measurements with glucose dehydrogenase (GD)-based and glucose oxidase (GO)-based test strips, to quantitate changes in glucose measurements observed with different Po2 levels, and to discuss the potential risks of oxygen-derived glucose errors in critical care. DesignVenous blood from healthy volunteers was tonometered to create different oxygen tensions simulating patient arterial Po2 levels. Venous blood from diabetic patients was exposed to air to alter oxygen tensions simulating changes in Po2 during sample handling. Whole-blood glucose measurements obtained from these samples with six glucose meters were compared with reference analyzer plasma glucose measurements. Glucose differences were plotted vs. different Po2 levels to identify error trends. Error tolerances were as follows: a) within ±15 mg/dL of the reference measurement for glucose levels ≤100 mg/dL; and b) within ±15% of the reference measurement for glucose levels >100 mg/dL. Setting and Subjects Five healthy volunteers in the bench study and 11 diabetic patients in the clinical study. ResultsIn the bench study, increases in Po2 levels decreased glucose measured with GO-based amperometric test strips, mainly at Po2 levels >100 torr. At nearly constant glucose concentrations, glucose meter systems showed large variations at low (39 torr) vs. high (396 torr) Po2 levels. Glucose measured with GD-based amperometric and GO-based photometric test strips generally were within error tolerances. In the clinical study, 31.6% (Precision PCx), 20.2% (Precision QID), and 23.0% (Glucometer Elite) of glucose measurements with GO-based amperometric test strips, 14.3% (SureStep) of glucose measurements with GO-based photometric test strips, and 4.6% (Accu-Chek Advantage H) and 5.9% (Accu-Chek Comfort Curve) of glucose measurements with GD-based amperometric test strips were out of the error tolerances. ConclusionsDifferent oxygen tensions do not significantly affect glucose measured with the GD-based amperometric test strips, and have minimal effect on GO-based photometric test strips. Increases in oxygen tension lowered glucose measured with GO-based amperometric test strips. We recommend that the effects of different oxygen tensions in blood samples on glucose measurements be minimized by using oxygen-independent test strips for point-of-care glucose testing in critically ill and other patients with high or unpredictable blood Po2 levels.

Multiplex polymerase chain reaction detection enhancement of bacteremia and fungemia.

Objective:To test a multiplex real-time polymerase chain reaction (PCR) method for simultaneous detection of multiple organisms in bloodstream infections. Methods:Prospective observational study at the University of California Davis Medical Center (Sacramento, CA). Two hundred adult (>18 yrs) patients from the emergency room, intensive care units, and general medicine wards at risk of a bloodstream infection and who manifested signs of systemic inflammatory response syndrome (SIRS). Whole blood samples for PCR testing were collected at the same time as blood culture (BC). PCR results were compared to blood and other culture results. Results:PCR detected potentially significant bacteria and fungi in 45 cases compared to 37 by BC. PCR detected the methicillin resistance (mecA) gene in all three culture-confirmed methicillin-resistant Staphylococcus aureus cases. More than 68% of PCR results were confirmed by blood, urine, and catheter culture. Independent clinical arbitrators could not rule out the potential clinical significance of organism(s) detected by PCR, but not by BC. PCR did not detect Enterococcus faecalis in five BC-confirmed cases. On average, seven patient samples could be tested simultaneously with the PCR method in 6.54 ± .27 hrs. Conclusions:Multiplex PCR detected potentially significant bacteria and fungi that were not found by BC. BC found organisms that were not detected by PCR. Despite limitations of both BC and PCR methods, PCR could serve as an adjunct to current culture methods to facilitate early detection of bloodstream infections. Early detection of microorganisms has the potential to facilitate evidence-based treatment decisions, antimicrobial selection, and adequacy of antimicrobial therapy.

Multicenter study of oxygen-insensitive handheld glucose point-of-care testing in critical care/hospital/ambulatory patients in the United States and Canada.

OBJECTIVES Existing handheld glucose meters are glucose oxidase (GO)-based. Oxygen side reactions can introduce oxygen dependency, increase potential error, and limit clinical use. Our primary objectives were to: a) introduce a new glucose dehydrogenase (GD)-based electrochemical biosensor for point-of-care testing; b) determine the oxygen-sensitivity of GO- and GD-based electrochemical biosensor test strips; and c) evaluate the clinical performance of the new GD-based glucose meter system in critical care/hospital/ambulatory patients. DESIGN Multicenter study sites compared glucose levels determined with GD-based biosensors to glucose levels determined in whole blood with a perchloric acid deproteinization hexokinase reference method. One site also studied GO-based biosensors and venous plasma glucose measured with a chemistry analyzer. Biosensor test strips were used with a handheld glucose monitoring system. Bench and clinical oxygen sensitivity, hematocrit effect, and precision were evaluated. SETTING The study was performed at eight U.S. medical centers and one Canadian medical center. PATIENTS There were 1,248 patients. RESULTS The GO-based biosensor was oxygen-sensitive. The new GD-based biosensor was oxygen-insensitive. GD-based biosensor performance was acceptable: 2,104 (96.1%) of 2,189 glucose meter measurements were within +/-15 mg/dL (+/-0.83 mmol/L) for glucose levels of < or = 100 mg/dL (< or = 5.55 mmol/L) or within +/-15% for glucose levels of > 100 mg/dL, compared with the whole-blood reference method results. With the GD-based biosensor, the percentages of glucose measurements that were not within the error tolerance were comparable for different specimen types and clinical groups. Bracket predictive values were acceptable for glucose levels used in therapeutic management. CONCLUSIONS The performance of GD-based, oxygen-insensitive, handheld glucose testing was technically suitable for arterial specimens in critical care patients, cord blood and heelstick specimens in neonates, and capillary and venous specimens in other patients. Multicenter findings benchmark the performance of bedside glucose testing devices. With the new +/-15 mg/dL --> 100 mg/dL --> +/-15% accuracy criterion, point-of-care systems for handheld glucose testing should score 95% (or better), as compared with the recommended reference method. Physiologic changes, preanalytical factors, confounding variables, and treatment goals must be taken into consideration when interpreting glucose results, especially in critically ill patients, for whom arterial blood glucose measurements will reflect systemic glucose levels.

Katrina, the Tsunami, and Point-of-Care Testing Optimizing Rapid Response Diagnosis in Disasters

We assessed how point-of-care testing (POCT), diagnostic testing at or near the site of patient care, can optimize diagnosis, triage, and patient monitoring during disasters. We surveyed 4 primary care units (PCUs) and 10 hospitals in provinces hit hardest by the tsunami in Thailand and 22 hospitals in Katrina-affected areas. We assessed POCT, critical care testing, critical values notification, demographics, and disaster responses. Limited availability and poor organization severely limited POCT use. The tsunami impacted 48 PCUs plus island and province hospitals, which lacked adequate diagnostic instruments. Sudden overload of critical victims and transportation failures caused excessive mortality. In New Orleans, LA, flooding hindered rescue teams that could have been POCT-equipped. US sea, land, and airborne rescue brought POCT instruments closer to flooded areas. Katrina demonstrated POCT value in disaster responses. We recommend handheld POCT, airborne critical care testing, and disaster-specific mobile medical units in small-world networks worldwide.

Effects of pH on glucose measurements with handheld glucose meters and a portable glucose analyzer for point-of-care testing.

OBJECTIVES To determine pH effects on glucose measurements obtained with the latest generation of glucose devices, to quantitate changes in glucose measurements obtained over a wide pH range, and to assess the potential clinical risks of pH effects with use of point-of-care glucose testing. DESIGN Paired differences of glucose measurements between pH-altered and parallel control samples with target pH 7.40 were calculated. SETTING A pH range of 6.94 to 7.84 was used to evaluate pH effects on glucose measurements in vitro with 6 handheld glucose meters and a portable glucose analyzer at both normal, 4.81 mmol/L (86.6 mg/dL), and high, 11.16 mmol/L (201 mg/dL), glucose levels. MAIN OUTCOME MEASURES Glucose measurements obtained from test samples and control samples were compared by calculating paired differences, which were plotted against pH to show pH effects on glucose meter measurements. RESULTS At the normal glucose level, different pH levels did not interfere significantly with glucose measurements. At the high glucose level, a trend whereby low pH decreased and high pH increased glucose measurements was observed on the Precision G and the Precision QID glucose meters. CONCLUSION Because of potential risk in diabetic patients with ketoacidosis and in other patients with acid-base disorders, we recommend that clinicians choose glucose devices carefully and interpret the measurements cautiously when point-of-care glucose testing is performed in critically ill patients with acidemia, alkalemia, or changing acid-base status.

Potential clinical utility of polymerase chain reaction in microbiological testing for sepsis

Objectives: To evaluate the potential improvement of antimicrobial treatment by utilizing a new multiplex polymerase chain reaction (PCR) assay that identifies sepsis-relevant microorganisms in blood. Design: Prospective, observational international multicentered trial. Setting: University hospitals in Germany (n = 2), Spain (n = 1), and the United States (n = 1), and one Italian tertiary general hospital. Patients: 436 sepsis patients with 467 episodes of antimicrobial treatment. Methods: Whole blood for PCR and blood culture (BC) analysis was sampled independently for each episode. The potential impact of reporting microorganisms by PCR on adequacy and timeliness of antimicrobial therapy was analyzed. The number of gainable days on early adequate antimicrobial treatment attributable to PCR findings was assessed. Measurements and Main Results: Sepsis criteria, days on antimicrobial therapy, antimicrobial substances administered, and microorganisms identified by PCR and BC susceptibility tests. Results: BC diagnosed 117 clinically relevant microorganisms; PCR identified 154. Ninety-nine episodes were BC positive (BC+); 131 episodes were PCR positive (PCR+). Overall, 127.8 days of clinically inadequate empirical antibiotic treatment in the 99 BC+ episodes were observed. Utilization of PCR-aided diagnostics calculates to a potential reduction of 106.5 clinically inadequate treatment days. The ratio of gainable early adequate treatment days to number of PCR tests done is 22.8 days/100 tests overall (confidence interval 15–31) and 36.4 days/100 tests in the intensive care and surgical ward populations (confidence interval 22–51). Conclusions: Rapid PCR identification of microorganisms may contribute to a reduction of early inadequate antibiotic treatment in sepsis.

Preventing Medical Errors in Point-of-Care Testing Security, Validation, Performance, Safeguards, and Connectivity

OBJECTIVES o prevent medical errors, improve user performance, and enhance the quality, safety, and connectivity (bidirectional communication) of point-of-care testing. PARTICIPANTS Group A included 37 multidisciplinary experts in point-of-care testing programs in critical care and other hospital disciplines. Group B included 175 professional point-of-care managers, specialists, clinicians, and researchers. The total number of participants equaled 212. EVIDENCE This study followed a systems approach. Expert specifications for prevention of medical errors were incorporated into the designs of security, validation, performance, and emergency systems. Additional safeguards need to be implemented through instrument software options and point-of-care coordinators. Connectivity will be facilitated by standards that eliminate deficiencies in instrument communication and device compatibility. Assessment of control features on handheld, portable, and transportable point-of-care instruments shows that current error reduction features lag behind needs. CONCENSUS PROCESS: Step 1: United States national survey and collation of group A expert requirements for security, validation, and performance. Step 2: Design of parallel systems for these functions. Step 3: Written critique and improvement of the error-prevention systems during 4 successive presentations to group B participants over 9 months until system designs stabilized into final consensus form. CONCLUSIONS The consensus process produced 6 conclusions for preventing medical errors in point-of-care testing: (1) adopt operator certification and validation in point-of-care testing programs; (2) implement security, validation, performance, and emergency systems on existing and new devices; (3) require flexible, user-defined error-prevention system options on instruments as a prerequisite to federal licensing of new diagnostic tests and devices; (4) integrate connectivity standards for bidirectional information exchange; (5) preserve fast therapeutic turnaround time of point-of-care test results; and (6) monitor invalid use, operator competence, quality compliance, and other performance improvement indices to reduce errors, thereby focusing on patient outcomes.(Arch Pathol Lab Med. 2001;1307-1315)