[Reliability of the measurement of glucose at the bedside of critical patients]

Reliability and accuracy of bedside capillary blood glucose measurement by glucometers compared to venous blood glucose in critically ill patients: A facility based cross-sectional study

BACKGROUND

The traditional reference standard, venous blood glucose requires venipuncture and laboratories usually return the test results after 60 min. Our aim was to determine the agreement accuracy of glucose (capillary) levels obtained by POC glucometers with glucose (venous) values by standard laboratory method (glucose-oxidase) and to assess whether and to what extent the glucometers perform uniformly well across the entire range of blood glucose values.

METHODS

We compared the diagnostic accuracy of two-point of care glucometers with laboratory venous glucose, the reference standard using Bland-Altman plots and Clark error grid method to analyse the results.

RESULTS

This study included a total of 110 patients (38[34 %] women; mean age 52.1 years (SD, 17.3); range 14-85 years. Fourteen patients (12 %) were known to have diabetes. The mean glucose value (glucometer 1) was 152.9 mg/dL (SD 83.1); range = 48-501 mg/dL; that by glucometer 2 was 152.2 mg/dL (SD 76.2); range = 30-458 mg/dL and by the laboratory was 148.6 mg/dL (SD 81.5); range = 52-480 mg/dL. Of the 110 subjects, 2(2 %) had blood glucose below 70 mg/dL; 85(77 %) between 70 and 180 mg/dL and 23(21 %) had blood glucose exceeding 180 mg/dL. The Bland-Altman plot showed a bias of 4 mg% (95%CI -9.8 to +1.1); and the limits of agreement were -63 and + 54 mg%. The area under the receiver operating characteristic curve for the two glucometers was 0.92 and 0.93 respectively.

CONCLUSIONS

Point of care glucose, measured by glucometers was in agreement with the venous glucose estimation. Both glucometers were equally accurate and performed uniformly well across the wide range of blood glucose values.

Blood glucose monitoring in critically ill adult patients: type of sample and method of analysis. Systematic review and meta-analysis

INTRODUCTION

The clinical guideline for the management of sepsis, recommends using arterial blood samples for glycaemic control. A multicentre study in 86 Spanish intensive care units (ICU) revealed that 85.4% of ICUs used capillary puncture.

OBJECTIVE

To analyse the reliability of glycaemia by comparing different blood samples (arterial, venous, capillary) and instruments (glucometers, gasometers, central laboratory). Secondarily, to estimate the effect of confounding variables and the performance of measuring instruments as determined by different quality standards.

METHODOLOGY

Systematic review and meta-analysis with search in PubMed, CINAHL and Embase databases in September-2021 and September-2022, with no time or language limits. Grey literature sources: DART-Europe, OpenGrey and Google Scholar. Results summarised by qualitative (description of results, study characteristics) and quantitative (meta-analysis to assess standardised mean difference) synthesis. Methodological quality of articles assessed with Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2).

PROTOCOL

https://osf.io/ DOI 10.17605/OSF.IO/T8KYP.

RESULTS

A total of 32 articles and 5451 patients were included. No discrepancies were obtained between arterial glucometer vs laboratory samples [bias (95%CI): 0.01 (-0.12 to 0.14) mg/dL]. In contrast, arterial samples with a gasometer did significantly overestimate [bias (95%CI): 0.12 (0.01 to 0.24) mg/dL]. The same trend is seen in capillaries with a glucometer, although not significantly [bias (95%CI): 0.07 (--0.02 to 0.15) mg/dL]. There is discrepancy between studies on the effect of haematocrit and acid-base balance. The greatest consensus is on the poor agreement of glucometer with capillary vs laboratory samples in the presence of shock and vasopressor support, renal failure or during vitamin C treatment.

CONCLUSIONS

The evidence to date recommends the use of arterial blood with a blood glucose meter for better reliability of glycaemic analysis and less effect of possible confounding variables, frequently present in the critically ill adult patient.

Bedside Blood Glucose Monitoring in Critically Ill Patients: Comparison Between Arterial and Capillary Glucose

BACKGROUND

Critically ill patients are at high risk of hypoglycemia and are particularly vulnerable to unrecognized hypoglycemia. Close blood glucose monitoring is therefore crucial. There are several options to conduct frequent blood glucose measurement and a number of conditions in intensive care unit patients may affect the accuracy of blood glucose measurement. The aim of the study was to compare the accuracy of capillary glucose by bedside glucometer with arterial samples by bedside glucometer and arterial samples by blood gas analyzer in critically ill patients through a prospective case-control study.

MATERIALS AND METHODS

Arterial and capillary samples from 60 patients were taken simultaneously and were tested immediately at the bedside. Results of the paired measurements were compared and expressed as a correlation coefficient.

RESULTS

Capillary glucose in the study group and control group were 9.73 ± 2.28mmol/L and 8.9 ± 1.86mmol/L, respectively; mean arterial glucose measured by glucometer in the study group and control group were 9.25 ± 2.05mmol/L and 8.4 ± 1.89mmol/L, respectively; and mean arterial glucose measured by blood gas analyzer in the study group and control group were 8.41 ± 1.9mmol/L and 8.24 ± 1.5mmol/L, respectively. Correlation between capillary values and arterial values measured by glucometer was less in the study group (r = 0.936, P < 0.001 and r = 0.973, P < 0.001). Correlation between capillary values measured by glucometer and arterial values measured by blood gas analyzer was also less in the study group (r = 0.897, P = 0.001 and r = 0.964, P < 0.001).

CONCLUSIONS

Capillary blood glucose monitoring is reliable only in a selected group of critically ill patients.

Discrepancies between capillary glucose measurements and traditional laboratory assessments in both shock and non-shock states after trauma

INTRODUCTION

The purpose of this study was to analyze the accuracy of capillary blood glucose (CBG) against laboratory blood glucose (LBG) in critically ill trauma patients during the shock state.

METHODS

All critically ill trauma patients admitted to the Surgical Intensive Care Unit at the Los Angeles County + University of Southern California Medical Center requiring blood glucose monitoring from January 2007 to December 2008 were included. Accuracy of CBG was compared against LBG during shock and non-shock states. Shock was defined as either systolic blood pressure <90 mm Hg or mean arterial pressure <70 mm Hg and the need for vasopressor therapy. The Bland-Altman method was used to determine the agreement between CBG and LBG during shock and non-shock states. CBG values were considered to disagree significantly with LBG values when the difference exceeded 15%.

RESULTS

During the 2-y study period, a total of 1215 patients were admitted to the Surgical Intensive Care Unit. Overall, the mean age was 38.4 ± 20.9 y, 79.6% (967) were male, and 75.0% (911) sustained blunt trauma. A total of 1935 paired samples of CBG and LBG were included in this analysis (367 during shock and 1568 during non-shock). During shock, the mean difference between CBG and LBG levels was 13.4 mg/dL (95% CI, -15.4 to 42.2 mg/dL), and the limits of agreement were -27.1 and 53.9 mg/dL. A total of 136 CBG values (37.1%) differed from the LBG values by more than 15%. During non-shock, the mean difference between CBG and LBG levels was 12.6 mg/dL (95% CI, -19.9 to 32.5 mg/dL), and the limits of agreement were -20.6 and 45.8 mg/dL. A total of 639 CGB values (40.8%) differed from the LBG values by more than 15%. Agreement was lowest among hypoglycemic readings in both shock and non-shock states.

CONCLUSION

There is poor correlation between the capillary and laboratory glucose values in both shock and non-shock states.

Tale of two sites: capillary versus arterial blood glucose testing in the operating room

INTRODUCTION

Pre- and intraoperative glycemic control has been identified as a putative target to improve outcomes of surgical patients. Glycemic control requires frequent monitoring of blood glucose levels with appropriate adjustments. However, monitoring standards have been called into question, especially in cases in which capillary samples are used. Point-of-care testing (POCT) using capillary samples and glucometers has been noted to give relatively accurate results for critically ill patients. However, the package inserts of most glucometers warn that they should not be used for patients in shock. This has led clinicians to doubt their accuracy in the operating room. The accuracy of capillary samples when tested in patients undergoing surgical procedures has not been proven. This study aims to determine the accuracy of intraoperative blood glucose values using capillary samples relative to arterial samples.

METHODS

A prospective study was conducted by collecting paired capillary and arterial samples of patients undergoing major operations at a tertiary medical center from August 2009 to May 2011. Subjects were a convenience sample of patients who had arterial lines and needed glucose testing while undergoing the procedure. Precision Xceed Pro (Abbott) handheld glucometers were used to obtain the blood glucose values. Our primary outcome of interest was the degree of correlation between capillary and arterial blood glucose values or the degree to which arterial glucose levels can be predicted by capillary glucose samples. We used linear regression and the Student t tests for statistical analyses.

RESULTS

Seventy-two-paired samples were collected. Of the cases, 54% were major abdominal operations, whereas 24% were vascular operations. The mean values ± standard deviation for glucose levels were 146 ± 35 mg/dL (capillary) and 147 ± 36 mg/dL (arterial). The mean time ± standard deviation between the collection of both samples was 3.5 ± 1.3 minutes. The regression coefficient showed a strong positive correlation of .91 between capillary glucose values and arterial values (P < .001) although correlation was less stringent at the hyperglycemic range of values. The R(2) statistic was 84%. Differences in values between capillary and arterial samples would not have altered the diagnosis of hypo- and hyperglycemia using typical thresholds.

CONCLUSIONS

Capillary samples collected intraoperatively are strongly correlated with arterial samples. Glucose monitoring in the operating room can be safely performed by collecting capillary samples for POCT. However, clinicians should still be cautious when interpreting glucose levels that are high, either by repeating the blood glucose test or by having samples sent to the laboratory.

Anemia causes hypoglycemia in intensive care unit patients due to error in single-channel glucometers: methods of reducing patient risk

OBJECTIVE

Intensive insulin therapy in the critically ill reduces mortality but carries the risk of increased hypoglycemia. Point-of-care blood glucose analysis is standard; however, anemia causes falsely high values and potentially masks hypoglycemia. Permissive anemia is practiced routinely in most intensive care units. We hypothesized that point-of-care glucometer error due to anemia is prevalent, can be corrected mathematically, and correction uncovers occult hypoglycemia during intensive insulin therapy.

DESIGN

The study has both retrospective and prospective phases. We reviewed data to verify the presence of systematic error, determine the source of error, and establish the prevalence of anemia. We confirmed our findings by reproducing the error in an in vitro model. Prospective data were used to develop a correction formula validated by the Monte Carlo method. Correction was implemented in a burn intensive care unit and results were evaluated after 9 mos.

SETTING

Burn and trauma intensive care units at a single research institution.

PATIENTS/SUBJECTS

Samples for in vitro studies were taken from healthy volunteers. Samples for formula development were from critically ill patients who received intensive insulin therapy.

INTERVENTIONS

Insulin doses were calculated based on predicted serum glucose values from corrected point-of-care glucometer measurements.

MEASUREMENTS AND MAIN RESULTS

Time-matched point-of-care glucose, laboratory glucose, and hematocrit values. We previously found that anemia (hematocrit <34%) produces systematic error in glucometer measurements. The error was correctible with a mathematical formula developed and validated, using prospectively collected data. Error of uncorrected point-of-care glucose ranged from 19% to 29% (p < .001), improving to < or = 5% after mathematical correction of prospective data. Comparison of data pairs before and after correction formula implementation demonstrated a 78% decrease in the prevalence of hypoglycemia in critically ill and anemic patients treated with insulin and tight glucose control (p < .001).

CONCLUSIONS

A mathematical formula that corrects erroneous point-of-care glucose values due to anemia in intensive care unit patients reduces the prevalence of hypoglycemia during intensive insulin therapy.