Assessing Point-of-Care Hemoglobin Measurement

Accuracy of point-of-care testing devices for haemoglobin in the operating room: meta-analysis

BACKGROUND

Point-of-care tests (POCT) for haemoglobin are increasingly used to guide intraoperative transfusion. However, their accuracy compared to central laboratory tests is unknown. The objective was to perform a systematic review and meta-analysis of method comparison studies assessing the accuracy of POCT versus central laboratory haemoglobin tests in patients undergoing surgery.

METHODS

Electronic databases were searched from inception to April 2020 (updated August 2023). Any methodological approach comparing haemoglobin measurements between POCT and central laboratory in patients undergoing surgery under anaesthesia in the operating room were included. Data abstraction was guided by PRISMA and risk of bias was assessed by QUADAS-2. Data were extracted independently and in duplicate by two reviewers. Outcomes included mean differences between POCT and central laboratory haemoglobin with associated standard deviations and 95% limits of agreement (LOA).

RESULTS

Of 3057 citations, 34 studies were included (n = 2427, 6857 paired measurements). Several devices were compared (pulse co-oximetry, n = 25; HemoCue, n = 10; iSTAT, n = 6; blood gas analysers, n = 10; haematology analyser, n = 2). Median sample size was 41 patients, and 11 studies were funded by device manufacturers. Fifteen of 34 studies had low risk of bias. Pooled mean differences (95% LOA) were: pulse co-oximeters 2.3 g/l (-25.2-29.8), HemoCue -0.3 g/l (-11.1-10.5), iSTAT -0.3 g/l (-8.4-7.8) and blood gas analysers -2.6 g/l (-17.8-12.7).

CONCLUSION

All POCT examining intraoperative haemoglobin measurement yielded pooled mean difference LOAs larger than the allowable limit difference of ±4 g/dl. Intraoperative haemoglobin measured by POCT should not be considered interchangeable with central laboratory values and caution is necessary when using these tests to guide intraoperative transfusion.

Point-of-care haemoglobin accuracy and transfusion outcomes in non-cardiac surgery at a Canadian tertiary academic hospital: protocol for the PREMISE observational study

INTRODUCTION

Transfusions in surgery can be life-saving interventions, but inappropriate transfusions may lack clinical benefit and cause harm. Transfusion decision-making in surgery is complex and frequently informed by haemoglobin (Hgb) measurement in the operating room. Point-of-care testing for haemoglobin (POCT-Hgb) is increasingly relied on given its simplicity and rapid provision of results. POCT-Hgb devices lack adequate validation in the operative setting, particularly for Hgb values within the transfusion zone (60-100 g/L). This study aims to examine the accuracy of intraoperative POCT-Hgb instruments in non-cardiac surgery, and the association between POCT-Hgb measurements and transfusion decision-making.

METHODS AND ANALYSIS

PREMISE is an observational prospective method comparison study. Enrolment will occur when adult patients undergoing major non-cardiac surgery require POCT-Hgb, as determined by the treating team. Three concurrent POCT-Hgb results, considered as index tests, will be compared with a laboratory analysis of Hgb (lab-Hgb), considered the gold standard. Participants may have multiple POCT-Hgb measurements during surgery. The primary outcome is the difference in individual Hgb measurements between POCT-Hgb and lab-Hgb, primarily among measurements that are within the transfusion zone. Secondary outcomes include POCT-Hgb accuracy within the entire cohort, postoperative morbidity, mortality and transfusion rates. The sample size is 1750 POCT-Hgb measurements to obtain a minimum of 652 Hgb measurements <100 g/L, based on an estimated incidence of 38%. The sample size was calculated to fit a logistic regression model to predict instances when POCT-Hgb are inaccurate, using 4 g/L as an acceptable margin of error.

ETHICS AND DISSEMINATION

Institutional ethics approval has been obtained by the Ottawa Health Science Network-Research Ethics Board prior to initiating the study. Findings from this study will be published in peer-reviewed journals and presented at relevant scientific conferences. Social media will be leveraged to further disseminate the study results and engage with clinicians.

Comparison of two point-of-care measurements of hemoglobin against standard laboratory values during pediatric liver transplantation: A retrospective review

BACKGROUND

Point-of-care hemoglobin testing devices play an important role in intraoperative anesthetic management where significant hemorrhage is anticipated; however, the reliability of these devices has not been examined in the context of pediatric liver transplantation. In this retrospective observational study, we aimed to determine whether 95% of results from two point-of-care hemoglobinometers, the HemoCue and iSTAT, would fall within a difference of ±1 g/dl, our a priori-defined clinically acceptable level of agreement, of the hemoglobin measures on a core laboratory complete blood count.

METHODS

We retrospectively collected data from 70 patients presenting for a liver transplant at a single center, tertiary care pediatric hospital over a 3.5-year period. We analyzed 92 contemporaneous pairs of hemoglobin values from the HemoCue and complete blood count, and 252 pairs of hemoglobin values from the iSTAT and complete blood count. Agreement between the point-of-care devices and complete blood count was assessed using Bland-Altman analysis, which was the primary outcome. Secondary analyses included an error grid analysis and Cohen's kappa statistic.

RESULTS

Both point-of-care devices underestimated complete blood count hemoglobin values and neither device satisfied our a priori-defined clinically acceptable level of agreement that 95% of values would fall within ±1 g/dl of the complete blood count measurement. The mean difference [limits of agreement] of the HemoCue was 0.4 g/dl (p < .001) [-0.9 to 1.6 g/dl] and of the iSTAT was 0.6 g/dl (p < .001) [-1.4 to 2.6 g/dl]. Secondary error grid analysis revealed that neither device performed well enough to replace a complete blood count at critical thresholds of hemoglobin values.

CONCLUSIONS

While the HemoCue and iSTAT contribute information in a timely manner during dynamic intraoperative situations, there is significant imprecision compared to the gold standard complete blood count. If clinical stability allows, the results of these point-of-care hemoglobinometers should be confirmed with a complete blood count, rather than being used as the sole factor in determining transfusion needs during pediatric liver transplantation.

Comparison of Hemoglobin Measurements by 3 Point-of-Care Devices With Standard Laboratory Values and Reliability Regarding Decisions for Blood Transfusion

BACKGROUND

We compared the accuracy of 3 point-of-care testing (POCT) devices with central laboratory measurements and the extent to which between-method disagreements could influence decisions to transfuse blood.

METHODS

Hemoglobin concentrations [Hb] were measured in 58 adult patients undergoing cardiothoracic surgery using 2 Ilex GEM Premier 3500 blood gas analyzers (BG_A and BG_B) and a HemoCue Hb-201 device (HemoCue). Measurements were compared with our central laboratory's Siemens Advia 2120 flow cytometry system (laboratory [Hb] [Lab[Hb]]), regarded as the gold standard. We considered that between-method [Hb] differences exceeding 10% in the [Hb] range 6-10 g/dL would likely erroneously influence erythrocyte transfusion decisions.

RESULTS

The 70 Lab[Hb] measurements ranged from 5.8 to 16.7 g/dL, of which 25 (36%) were <10.0 g/dL. Measurements by all 4 devices numbered 57. Mean POCT measurements did not differ significantly (P > .99). Results of the Bland-Altman analyses revealed statistically significant bias, with predominant underestimations by all 3 POCTs predominating. HemoCue upper and lower limits of agreement (LOA) were narrower, and the 95% confidence intervals (95% CIs) of the LOAs did not overlap with those of BG_A and BG_B. Similarly, a narrow mountain plot demonstrated greater precision for the HemoCue. Comparing BG_A with BG_B revealed no bias and narrow LOA. Error grid analysis within the [Hb] range 6-10 g/dL revealed that 5.3% of HemoCue measurements were beyond the permissible 10.0% error zone in contrast to 19.0% and 16.0% of the blood gas measurements. Possible inappropriate transfusion decisions based on POCT values generally erred toward unnecessary transfusions. Calculations of Cohen κ statistic indicated better chance-corrected agreement between HemoCue and Lab[Hb] regarding erythrocyte transfusions than the blood gas analyzers.

CONCLUSIONS

All 3 POCT devices underestimated the Lab[Hb] and cannot be used interchangeably with standard laboratory measurements. BG_A and BG_B can be considered to be acceptably interchangeable with each other. Whereas the HemoCue had little bias and good precision, the blood gas analyzers revealed large bias and poor precision. We conclude that the tested HemoCue provides more reliable measurements, especially within the critical 6-10 g/dL range, with reduced potential for transfusion errors. Decisions regarding erythrocyte transfusions should also be considered in the light of clinical findings.

Clinical implications of using non-invasive haemoglobin monitoring for red blood cell transfusion decision in hip arthroplasty

INTRODUCTION

The decision to transfuse red blood cells requires accurate haemoglobin concentration values. In this study, we evaluated if continuous non-invasive haemoglobin (SpHb) measurement could substitute laboratory determined haemoglobin (LabHb) in patients undergoing elective hip replacement. As secondary objective, we analyzed the trend of the difference between techniques.

MATERIALS/METHODS

LabHb measurements were done using an automated analyser and SpHb measurements were acquired using Radical-7®. In randomly selected patients undergoing hip replacement, whenever blood was collected for LabHb, concomitant SpHb was recorded. Correlation, bias and accuracy of SpHb were calculated in comparison with LabHb.

RESULTS

108 paired measurements were obtained from 43 patients. The Pearson R of the correlation between SpHb and LabHb was 0.7 (p < 0.001). Bland-Altman test revealed a bias of 1 ± 1.4 g dL^-1, meaning Lab Hb was recurrently higher than SpHb. Limits of agreement were [-1.7; 3.8]. Considering RBC transfusion threshold of 8 g dL^-1, we found that in two situations transfusion decision would differ based on the measurement considered. Trending ability of SpHb study showed a significant difference between preoperative and postoperative LabHb-SpHb.

DISCUSSION

There was a good correlation between SpHb and LabHb, while bias and limits of agreement were higher than those in literature. There was a limited trending ability of SpHb during the perioperative period. Despite this, using SpHb instead of LabHb for decision making regarding transfusion would only change the decision in 1.9 % of our cases. Our findings suggest that this device could be used as a reference but cannot replace venous puncture as gold standard.

Continuous Noninvasive Hemoglobin Monitoring: A Measured Response to a Critical Review

Supplemental Digital Content is available in the text.

Published ahead of print March 5, 2015

A comparison of hemoglobin measured by co-oximetry and central laboratory during major spine fusion surgery

BACKGROUND

Many factors affect the accuracy of hemoglobin concentration values. In this study, we evaluated whether the hemoglobin concentration obtained by means of arterial blood gas (ABG) co-oximetry and complete blood count (CBC) central laboratory techniques clinically correlate when using simultaneous measurements of hemoglobin concentration obtained during complex spine fusion surgery.

METHODS

Three hundred forty-eight patients who underwent spinal fusion of >3 bony levels between September 2006 and September 2010, with concurrent ABG and CBC samples, were identified. The mean difference between pairs of measured hemoglobin values was determined using limits of agreement analysis. Error grid analysis was used to delineate correlation of samples in relation to hemoglobin values within the range considered for transfusion.

RESULTS

The median difference (ABG-CBC) between the measured hemoglobin values was 0.4 g/dL (95% confidence interval [CI], 0.35-0.40 g/dL; P < 0.0001). Limits of agreement analysis correcting for repeated observations in multiple patients demonstrated that the mean difference between measured hemoglobin values (i.e., bias) was 0.4 g/dL (95% CI, 0.36-0.41 g/dL), and the 95% limits of agreement of the difference between paired measurements were -0.70 to 1.47 g/dL. The magnitude of the difference between the measured hemoglobin values was >0.5 g/dL in 44.5% of patients (95% CI, 42.2%-46.8%); however, 6.8% (95% CI, 5.8%-8.1%) of paired measurements had a difference of >1.0 g/dL. There was only fair-to-moderate agreement between the CBC and ABG values within the clinically significant range of hemoglobin values of 7 to 10 g/dL (Cohen κ = 0.39; 95% CI, 0.33-0.45).

CONCLUSIONS

The hemoglobin values obtained from ABG and CBC cannot be used interchangeably when verifying accuracy of novel point-of-care hemoglobin measurement modalities or when managing a patient with critical blood loss.

Comparison of Massimo Pronto-7 and Hemocue Hb 201+ with Laboratory Haemoglobin Estimation: A Clinical Study

We prospectively studied agreement in haemoglobin estimation between two point-of-care devices (Pronto-7® Pulse CO-Oximetry™, Masimo Corporation, Irvine, California, USA and HemoCue® Hb 201+, HemoCue, Angelholm, Sweden) and an automated laboratory analyser (Sysmex XE5000, Sysmex Corporation, Kobe, Japan). Venous blood sampling and finger co-oximeter readings were performed on 141 pregnant women undergoing routine mid-trimester haemoglobin assessment. Three replicate measures were performed and analysis used Bayesian-based variance component modelling to provide estimates of repeatability, between person within method bias and precision. Repeatability, assessed by coefficient of variation, was higher for Pronto-7® (2.3%) compared to HemoCue® (5.2%). Fixed bias (mean difference, device - laboratory) was +1.18 (standard deviation 1.19) g/dl and - 0.01 (standard deviation 1.34) g/dl for Pronto-7® and HemoCue® respectively, with no statistical evidence of proportional bias. Based upon a single device reading, the 95% prediction limits for Pronto-7® were −1.2 to 3.6 g.dl-1 and HemoCue® were −2.7 to 2.7 g/dl. For both devices precision was not meaningfully improved by averaging replicate readings. However, repeated readings may allow detection of aberrant results. Overall both devices are imprecise and 95% prediction limits wide. We present further prediction limits, derived from the posterior distribution and adjusted for any fixed bias for set levels of probability (certainty). These may be used to support clinical decisions when using these point-of-care devices.

Accuracy of Noninvasive and Continuous Hemoglobin Measurement by Pulse Co-Oximetry During Preoperative Phlebotomy

Background:

In recent years, the continuous noninvasive hemoglobin measurement has been offered by devices using advanced pulse oximetry technology. Accuracy has been established in healthy adults as well as in surgical and intensive care unit patients but not in the setting of acute hemorrhage. In this study, we evaluated the accuracy of such a device in the clinical setting of preoperative phlebotomy thereby mimicking a scenario of acute blood loss.

Methods:

This prospective study included patients undergoing surgical repair of congenital heart disease (CHD) for whom preoperative phlebotomy was planned. Blood was removed after the induction of anesthesia and prior to the start of the surgical procedure. Replacement with crystalloid was guided by hemodynamic variables and cerebral oxygenation measured by near-infrared spectroscopy. Hemoglobin was measured by bedside whole blood analysis (total hemoglobin [tHb]) before and after phlebotomy, and concurrent measurements from the pulse co-oximeter (noninvasive, continuous, or spot-check testing of total hemoglobin [SpHb]) were recorded.

Results:

The study cohort included 45 patients ranging in age from 3 months to 50 years. Preoperative phlebotomy removed an average of 9.2 mL/kg of blood that was replaced with an average of 7.2 mL/kg of crystalloid. The pre- and postphlebotomy tHb values were 13.0 ± 1.9 and 12.4 ± 1.8 g/dL, respectively. The absolute difference between the tHb and SpHb (▵Hb) was 1.2 ± 0.1 g/dL. Bland-Altman analysis revealed a bias of 0.1 g/dL, a precision of 1.5 g/dL, and 95% limits of agreement of −2.8 to 3.1 g/dL. In 52.2% of the sample sets, the SpHb was within 1 g/dL of the actual hemoglobin value (tHb), and in 80% of the sample sets, the SpHb was within 2 g/dL. No variation in the accuracy of the deviation was noted based on the patient’s age, weight, or type of CHD (cyanotic versus acyanotic).

Conclusion:

The current study demonstrates that the accuracy of continuous, noninvasive hemoglobin measurement was not affected by acute blood loss simulated by preoperative phlebotomy. Although the device provided a clinically acceptable correlation with the actual hemoglobin value and offers the value of a continuous trend monitor, given the precision of the device, it does not appear that actual transfusion decisions can be based on the device alone.

A comparison of lidocaine and bupivacaine digital nerve blocks on noninvasive continuous hemoglobin monitoring in a randomized trial in volunteers

BACKGROUND

Blood hemoglobin can be monitored continuously and noninvasively with a noninvasive spectrophotometric sensor (Masimo SpHb). The perfusion index (PI) of the finger is directly related to the clinical accuracy of SpHb. We evaluated those variables that influence PI without the influences of surgery and anesthesia.

METHODS

Based on our past studies, 12 awake adult volunteers were studied. A SpHb sensor was attached to the same finger of each hand. The temperature of each finger was measured via a skin surface probe. A digital nerve block (DNB) was performed with 1% lidocaine on one finger and 0.25% bupivacaine on the other finger of the opposite hand. SpHb, PI, and finger temperature were monitored continuously 30 minutes before and 3 to 4 hours after placement of the DNB. A random effects spline regression was used to flexibly model the outcomes before and after the DNB and to compare the effects of lidocaine and bupivacaine.

RESULTS

The DNBs increased the PI for both lidocaine and bupivacaine (P < 0.0001) and finger temperature from both lidocaine (P < 0.0001) and bupivacaine (P = 0.02). The duration of action of bupivacaine was markedly longer than that of lidocaine (P < 0.0001). Between 45 and 75 minutes after insertion of the DNB, the PI with bupivacaine was substantially higher than that of lidocaine. The PI was directly related to changes in finger temperature and SpHb. During this time interval, 11 of the 12 volunteers receiving bupivacaine descriptively had increases in finger temperature ranging from no change to 6.1°C. In contrast, only 6 of the 12 lidocaine volunteers had increases in finger temperature ranging from no change to 4°C. Changes in PI were directly correlated with SpHb values (correlation coefficient = 0.7).

CONCLUSIONS

A DNB increases PI and finger temperature. These increases lasted 2 to 3 hours longer with bupivacaine than lidocaine. The increases in PI were associated with slightly higher SpHb values. We conclude that the DNB induces increases in PI and temperature of the finger. Because of the close relationship between finger temperature, PI, and SpHb, consistently increasing finger temperature and PI could increase the accuracy of SpHb.

Accuracy of point-of-care glucose measurements

Control of blood glucose (BG) in an acceptable range is a major therapy target for diabetes patients in both the hospital and outpatient environments. This review focuses on the state of point-of-care (POC) glucose monitoring and the accuracy of the measurement devices. The accuracy of the POC glucose monitor depends on device methodology and other factors, including sample source and collection and patient characteristics. Patient parameters capable of influencing measurements include variations in pH, blood oxygen, hematocrit, changes in microcirculation, and vasopressor therapy. These elements alone or when combined can significantly impact BG measurement accuracy with POC glucose monitoring devices (POCGMDs). In general, currently available POCGMDs exhibit the greatest accuracy within the range of physiological glucose levels but become less reliable at the lower and higher ranges of BG levels. This issue raises serious safety concerns and the importance of understanding the limitations of POCGMDs. This review will discuss potential interferences and shortcomings of the current POCGMDs and stress when these may impact the reliability of POCGMDs for clinical decision-making.