Increased plasma glucose levels after change of recommendation from NaF to citrate blood collection tubes

How pre-analytical conditions impact glucose measurement and (gestational) diabetes diagnosis: A real-world stability study and a call for harmonization

BACKGROUND AND AIMS

Since 2023, guidelines of the AACC/ADA recommend the use of citrate buffer-containing tubes as a first option for glucose measurement. This study aims to assess the pre-analytical stability of glucose under various conditions (room temperature (RT) or at 4 °C) and the potential real-world impact of introducing these tubes on (gestational) diabetes and IFG prevalence.

MATERIALS AND METHODS

25 healthy volunteers were sampled to assess glucose stability across time, at 4 °C and at RT, before and following centrifugation. 701 patients undergoing fasting plasma glucose analysis and 109 women having OGTT were collected according to current procedures (NaFl K2C2O4 (NaFl) tubes) as well as with citrate-containing tubes (FC Mix).

RESULTS

The mean glucose concentration bias between FC Mix and NaFl tubes when centrifugation occurred within 5 min was 0.53 % and this difference raised slowly to reach 2.3 %, six-hours post-centrifugation. When centrifugation was delayed, a rapid decrease in glucose concentrations was observed for NaFl tubes (4.9 % at 30 min) and this trend was only partially reduced by placing samples at 4 °C (3.1 %). The decrease reached 10.8 % (RT) and 7.8 % (4 °C) at 2 h, before reaching a plateau. Samples collected on citrate remained stable during 24 h. In real-life conditions, the mean bias between FC Mix and NaFl tubes increased progressively over time and reached 8.59 % for samples centrifuged between two- and four-hours following sampling. Compared to widespread practices, the use of citrate-containing tubes increased IFG, DM and GDM prevalences by 84.0 %, 36.7 % and 150 %, respectively.

CONCLUSIONS

Glucose concentrations rapidly decrease in NaFl tubes following collection and placing samples at 4 °C reduces only marginally the decay. Citrate-containing tubes offer a valuable solution for direct and long-lasting glucose stabilization but, before wider adoption, large epidemiologic studies should confirm or redefine current diabetes diagnostic thresholds.

Plasma Glucose Concentrations in Different Sampling Tubes Measured on Different Glucose Analysers

INTRODUCTION

The German Diabetes Association recommends using sampling tubes with citrate and fluoride additives to diagnose diabetes by oral glucose tolerance test to inhibit glycolysis. The effect of different tubes on measurement results was assessed.

MATERIALS AND METHODS

In a first study, an oral glucose tolerance test was performed on 41 participants without anamnestically known diabetes. Venous blood was sampled in two different tubes with citrate/fluoride additives from different manufacturers and one with only lithium-heparin additive. A second study with 42 participants was performed to verify the initial results with an adapted design, in which a third tube with citrate buffer was used, and glucose measurements were performed on two additional devices of another analyser model. Samples were centrifuged either immediately (<5 min incubation time) or after 20 min or 4 h. All glucose measurements were performed in plasma. Glucose concentrations in lithium-heparin tubes with<5 min incubation time served as baseline concentrations.

RESULTS

In the first study, glucose concentrations in one of the citrate/fluoride tubes were similar to the baseline. In the other citrate/fluoride tube, markedly lower concentrations (approximately - 5 mg/dL (- 0.28 mmol/L)) were measured. This was reproduced in the verification study for the same analyser, but not with the other analyser model. Lithium-heparin tubes centrifuged after 20 and 240 min showed systematically lower glucose concentrations.

CONCLUSIONS

The results confirm that glycolysis can be effectively inhibited in citrate/fluoride-containing sampling tubes. However, glucose measurement results of one analyser showed a relevant negative bias in tubes containing liquid citrate buffer.

Precise glucose measurement in sodium fluoride-citrate plasma affects estimates of prevalence in diabetes and prediabetes

OBJECTIVES

Estimates of glucose concentrations vary among types of blood samples, which impact on the assessment of diabetes prevalence. Guidelines recommend a conversion factor to calculate plasma glucose from measurements of glucose in whole blood. The American Diabetes Association recommends the use of blood drawing tubes containing sodium fluoride (NaF) and citrate, which have not yet been evaluated regarding possible differences in glucose concentration and conversion factors. Thus, we compared glucose measurements in NaF-citrate plasma and venous whole blood and estimated the impact of differences on diabetes and prediabetes prevalence.

METHODS

Glucose differences were calculated by Bland-Altman analysis with pairwise comparison of glucose measurements from whole blood and NaF-citrate plasma (n=578) in clinical studies of the German Diabetes Center. Subsequently, we computed the impact of the glucose difference on diabetes and prediabetes prevalence in the population-based National Health and Nutrition Examination Survey (NHANES).

RESULTS

Even upon conversion of whole blood to plasma glucose concentrations using the recommended conversion factor, mean glucose concentration difference remained 4.72 % higher in NaF-citrate plasma. Applying the higher glucose estimates, increases the population-based diabetes and prediabetes prevalence by 13.67 and 33.97 % or more than 7.2 and 13 million people in NHANES, respectively. Additional economic burden could be about 20 $ billion per year due to undiagnosed diabetes.

CONCLUSIONS

The recommended conversion factor is not valid for NaF-citrate plasma. Systematic bias of glucose measurements due to sampling type leads to clinically relevant higher estimates of diabetes and prediabetes prevalence.

Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus

BACKGROUND

Numerous laboratory tests are used in the diagnosis and management of diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially.

APPROACH

An expert committee compiled evidence-based recommendations for laboratory analysis in screening, diagnosis, or monitoring of diabetes. The overall quality of the evidence and the strength of the recommendations were evaluated. The draft consensus recommendations were evaluated by invited reviewers and presented for public comment. Suggestions were incorporated as deemed appropriate by the authors (see Acknowledgments). The guidelines were reviewed by the Evidence Based Laboratory Medicine Committee and the Board of Directors of the American Association for Clinical Chemistry and by the Professional Practice Committee of the American Diabetes Association.

CONTENT

Diabetes can be diagnosed by demonstrating increased concentrations of glucose in venous plasma or increased hemoglobin A1c (HbA1c) in the blood. Glycemic control is monitored by the people with diabetes measuring their own blood glucose with meters and/or with continuous interstitial glucose monitoring (CGM) devices and also by laboratory analysis of HbA1c. The potential roles of noninvasive glucose monitoring, genetic testing, and measurement of ketones, autoantibodies, urine albumin, insulin, proinsulin, and C-peptide are addressed.

SUMMARY

The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are found to have minimal clinical value at the present time, and measurement of them is not recommended.

Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus

BACKGROUND

Numerous laboratory tests are used in the diagnosis and management of diabetes mellitus. The quality of the scientific evidence supporting the use of these assays varies substantially.

APPROACH

An expert committee compiled evidence-based recommendations for laboratory analysis in screening, diagnosis, or monitoring of diabetes. The overall quality of the evidence and the strength of the recommendations were evaluated. The draft consensus recommendations were evaluated by invited reviewers and presented for public comment. Suggestions were incorporated as deemed appropriate by the authors (see Acknowledgments). The guidelines were reviewed by the Evidence Based Laboratory Medicine Committee and the Board of Directors of the American Association of Clinical Chemistry and by the Professional Practice Committee of the American Diabetes Association.

CONTENT

Diabetes can be diagnosed by demonstrating increased concentrations of glucose in venous plasma or increased hemoglobin A1c (Hb A1c) in the blood. Glycemic control is monitored by the people with diabetes measuring their own blood glucose with meters and/or with continuous interstitial glucose monitoring (CGM) devices and also by laboratory analysis of Hb A1c. The potential roles of noninvasive glucose monitoring, genetic testing, and measurement of ketones, autoantibodies, urine albumin, insulin, proinsulin, and C-peptide are addressed.

SUMMARY

The guidelines provide specific recommendations based on published data or derived from expert consensus. Several analytes are found to have minimal clinical value at the present time, and measurement of them is not recommended.

Impact of optimizing pre-analytical phase on the diagnosis of gestational diabetes and related outcomes

OBJECTIVES

Pre-analytical plasma glucose (PG) sampling methodology may significantly affect gestational diabetes mellitus (GDM) incidence, but no studies directly examined the impact on perinatal outcomes. We compared the effect on oral glucose tolerance test (OGTT) results of using for blood sampling the traditional sodium fluoride (NaF) tubes, batched at controlled temperature, and the more effective citrate-buffered tubes, in terms of GDM diagnosis and related outcomes.

METHODS

We evaluated 578 pregnant women performing OGTT between 24- and 28-weeks' gestation. Paired NaF and citrate blood samples were drawn and analyzed for PG. GDM diagnosis was made by applying the 'one-step' American Diabetes Association strategy. Data on perinatal outcomes were collected in a subset of 330 women who delivered in our hospital network.

RESULTS

Using the standard NaF approach, 69 (11.9%) GDM women were detected. Using citrate PG values, 90 women were additionally identified as GDM, increasing the GDM prevalence to 27.5%. Perinatal outcomes were analyzed according to the different diagnostic allocation (NaF-diagnosed GDM, additional citrate-diagnosed GDM, and no GDM). NaF-diagnosed GDM showed a higher incidence of large for gestational age (LGA) (p=0.034), and of cesarean and preterm delivery (p<0.01) vs. no GDM. The only outcome remaining more frequent in the additional citrate diagnosed GDM when compared with no GDM group was LGA (17.2 vs. 6.8%, p=0.025).

CONCLUSIONS

If a health care system plans to use citrate tubes for GDM diagnosis, considerations about clinical implications are mandatory by balancing higher sensitivity in detecting a poor glycemic control with effects on outcomes to avoid "overdiagnosis".

Diagnosis of Gestational Diabetes Mellitus with Point-of-Care Methods for Glucose versus Hospital Laboratory Method Using Isotope Dilution Gas Chromatography-Mass Spectrometry as Reference

BACKGROUND

In Sweden, both glucose analyzers in accredited laboratories and point-of-care glucose devices are used for gestational diabetes mellitus (GDM) diagnosis. The aim of this study was to compare the diagnostic performance of the HemoCue Glucose 201+ (HC201+) and RT (HC201RT) systems with that of the hospital central laboratory hexokinase method (CL) based on lyophilized citrate tubes, using the isotope dilution gas chromatography-mass spectrometry (ID GC-MS) as reference.

METHODS

A 75 g oral glucose tolerance test was performed on 135 women screened positive for GDM. Diagnosis was based on the World Health Organization 2013 diagnostic thresholds for fasting (n = 135), 1 h (n = 135), 1 h (n = 135), 1 h (.

RESULTS

Significantly more women were diagnosed with GDM by HC201+ (80%) and CL (80%) than with the reference (65%, P < 0.001) based on fasting and/or 2 h thresholds, whereas the percentage diagnosed by HC201RT (60%) did not differ significantly from the reference. In Bland-Altman analysis, a positive bias was observed for HC201+ (4.2%) and CL (6.1%) and a negative bias for HC201RT (-1.8%). In the surveillance error grid, 95.9% of the HC201+ values were in the no-risk zone as compared to 98.1% for HC201RT and 97.5% for CL.

CONCLUSIONS

A substantial positive bias was found for CL measurements resulting in overdiagnosis of GDM. Our findings suggest better performance of HC201RT than HC201+ in GDM diagnosis. The results may have possible implications for GDM diagnosis in Sweden and require further elucidation.

Recommended pre-analytical plasma glucose sampling methodology may distort gestational diabetes mellitus prevalence: implications for diagnostic thresholds

AIM

Current International Association of the Diabetes and Pregnancy Study Groups/World Health Organization gestational diabetes mellitus (GDM) diagnostic thresholds are based on a landmark study in which the pre-analytical plasma glucose sampling methodology is unclear. Worldwide, plasma glucose pre-analytical sampling methodology practices are divergent. We considered the effects of pre-analytical plasma glucose sampling methodology on GDM prevalence and gestational outcomes.

METHODS

This is a retrospective observational cohort study of 1178 pregnant women undergoing an oral glucose tolerance test (OGTT). Of the 1178 pregnant women, a subset of 892 non-GDM women with singleton births undergoing OGTT between 24 and 28 weeks' gestation were investigated for large for gestation age (LGA) outcomes. OGTT were determined using traditional methods (sodium fluoride tubes batched at roomed temperature). We modelled the potential effects of using a recommended pre-analytical plasma glucose methodology (lyophilized citrate tubes) on GDM prevalence.

RESULTS

The GDM prevalence in our cohort was 13.5%. The incidence of LGA showed a linear association with maternal plasma glucose that was similar to the association observed in the Hyperglycemia and Adverse Pregnancy Outcome study. Frequency of LGA exceeded 10% at HAPO glucose category 4 (fasting, 4.8 to 4.9 mmol/l; 1-h, 8.7 to 9.5 mmol/l) for fasting and 1-h plasma glucose. The use of a recommended pre-analytical method is projected to increase the prevalence of GDM to 39.2%.

CONCLUSION

We challenge the consensus that recommended pre-analytical plasma glucose methodologies are optimal for the accurate diagnosis of GDM. Recommended pre-analytical plasma glucose methods may profoundly over-diagnose GDM. Centres using recommended pre-analytical plasma glucose methodologies may need to reappraise their diagnostic thresholds.

Clinical impact of citrate-containing tubes on the detection of glucose abnormalities by the oral glucose tolerance test

Background

Plasma glucose levels provide the cornerstone of diabetes evaluation, and so it is crucial that clinical laboratories provide accurate and reliable plasma glucose results. To prevent in vitro glycolysis, citrate is used. Here, we present the first study on the 75-g oral glucose tolerance test (OGTT) using the currently available new citrate-containing tubes in liquid and granular forms and the previous sodium fluoride (NaF) for the diagnosis of carbohydrate metabolism disorders and gestational diabetes mellitus (GDM) according to the American Diabetes Association (ADA) guidelines.

Methods

The 75-g OGTT was performed in 147 volunteers, 83 of whom were pregnant women. Blood was collected in NaF/K3 ethylenediaminetetraacetic acid (EDTA) and NaF/Na2EDTA/citrate in liquid form in tubes in Brescia and in NaF/K2Ox and NaF/Na2EDTA/citrate in granular form in Vicenza. Glucose was measured within 3–4 h from the OGTT. The mean biases were calculated and compared with the desirable bias (<± 2.1%).

Results

OGTT glucose concentrations were higher in citrate tubes when compared to NaF-containing tubes. When citrate tubes were used, GDM increased to 12.5 and 11.7% in Brescia and Vicenza, respectively. Impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and diabetes mellitus (DM) increased to 36.7, 6.7 and 3.4%, respectively, in Brescia. In Vicenza, an increase of 47 and 1.9% in IFG and IGT, respectively, was found.

Conclusions

OGTT glucose measurement in citrate-containing tubes was shown to be more effective than those containing only NaF in diagnosing carbohydrate disorders. This new glycolysis inhibitor seems to be a necessary preanalytical tool for accurate and reliable plasma glucose results.

Blood Glucose Determination: Effect of Tube Additives

The measurement of fasting plasma glucose may be biased by a time-dependent decrease of glucose in blood tubes, mainly attributable to blood cell metabolism when glycolysis is not rapidly inhibited or blood cells cannot be rapidly separated from plasma. Although glycolysis inhibitors such as sodium fluoride (NaF) in combination with potassium oxalate (KOx) are currently used for overcoming this drawback, their efficacy for stabilizing blood glucose is seemingly limited, and probably lower than that of newer additives such as the citrate buffer. Therefore, we performed a critical analysis of the current scientific literature aimed to generate evidence-based information about the advantages of using citrate buffer in blood tubes compared to the more conventional NaF additive. The results of our systematic overview of the literature show that citrate blood tubes represent a considerable step forward in achieving more accurate and reliable plasma glucose measurements, thereby limiting the risk of underdiagnosing diabetes due to spurious decrease of glucose concentration in uncentrifuged blood specimens, ensuring higher stability of glucose levels over time, while simultaneously producing less hemolysis compared to NaF blood tubes. Therefore, we suggest that the use of this new mixture should be encouraged for achieving a higher degree of accuracy and standardization of plasma glucose measurements.

Various glycolysis inhibitor-containing tubes for glucose measurement cannot be used interchangeably due to clinically unacceptable biases between them

Background:

The aim of our study was to determine the difference between glucose concentration measured 30 min after venipuncture in ice-chilled heparin plasma sample and all currently available citrate buffer-containing tubes (Greiner Glucomedics, Greiner FC Mix and Sarstedt GlucoEXACT) and still widely used sodium fluoride/potassium oxalate (NaF/Kox) tubes from Greiner.

Methods:

Blood was collected from 20 healthy volunteers and 20 patients with diabetes into LiH, NaF/KOx, Glucomedics, FC mix and GlucoEXACT tubes. Glucose was measured within 30 min from blood sampling in duplicate on the Architect c8000 analyzer. Mean biases between all tube types were calculated and compared to the recommended criteria (1.95%). Additionally, glucose concentrations measured in all five tube types were compared using the Friedman test.

Results:

In the entire studied population, glucose concentrations measured in Glucomedics, FC mix and GlucoEXACT were higher (7.3%, 3.2% and 2.0%, respectively) than in the ice-chilled LiH tubes. When all glycolysis inhibitor-containing tubes were compared, Glucomedics tubes significantly differed from GlucoEXACT and FC mix tubes (biases −4.9% and 4.0%, respectively). In addition, there was a significant difference between the NaF/KOx tube and Glucomedics, as well as FC mix tubes (biases 7.1% and 3.0%, respectively).

Conclusions:

Glucose concentrations measured in recommended ice-chilled lithium heparin- and citrate buffer-containing tubes are not comparable. Significant biases exist between various glycolysis inhibitor-containing tubes; therefore, they cannot be used interchangeably.

Pre-analytical and analytical aspects affecting clinical reliability of plasma glucose results

The measurement of plasma glucose (PG) plays a central role in recognizing disturbances in carbohydrate metabolism, with established decision limits that are globally accepted. This requires that PG results are reliable and unequivocally valid no matter where they are obtained. To control the pre-analytical variability of PG and prevent in vitro glycolysis, the use of citrate as rapidly effective glycolysis inhibitor has been proposed. However, the commercial availability of several tubes with studies showing different performance has created confusion among users. Moreover, and more importantly, studies have shown that tubes promptly inhibiting glycolysis give PG results that are significantly higher than tubes containing sodium fluoride only, used in the majority of studies generating the current PG cut-points, with a different clinical classification of subjects. From the analytical point of view, to be equivalent among different measuring systems, PG results should be traceable to a recognized higher-order reference via the implementation of an unbroken metrological hierarchy. In doing this, it is important that manufacturers of measuring systems consider the uncertainty accumulated through the different steps of the selected traceability chain. In particular, PG results should fulfil analytical performance specifications defined to fit the intended clinical application. Since PG has tight homeostatic control, its biological variability may be used to define these limits. Alternatively, given the central diagnostic role of the analyte, an outcome model showing the impact of analytical performance of test on clinical classifications of subjects can be used. Using these specifications, performance assessment studies employing commutable control materials with values assigned by reference procedure have shown that the quality of PG measurements is often far from desirable and that problems are exacerbated using point-of-care devices.

Overestimation of Hypoglycemia in Infants with a High Hematocrit

Background

In neonates, hypoglycemia is an emergency condition requiring urgent treatment. Therefore, rapid and reliable blood glucose measurements are necessary. However, this step has been proven difficult because of both analytical and preanalytical variables. In our children's hospital, we incidentally observed cases of hypoglycemia that were not in line with the clinical picture of the infants. Remarkably, most of these infants had a high hematocrit.

Methods

Glucose concentrations were determined in blood samples from healthy participants that were collected in Li-heparin capillary and pediatric tubes. The effect of hematocrit on glucose consumption over time was studied by artificially increasing sample hematocrits. To study the effect of sample cooling, glucose concentrations were followed over time in samples stored at room temperature and on ice.

Results

In all samples, glucose concentrations declined with time. This effect was most dramatic [up to 18 mg/dL (1 mmol/L) in the first 30 min] in samples with high hematocrits and collected in capillary tubes. Cooling of samples clearly reduced glucose consumption; however, this was not evident in the first 30 min.

Conclusions

Overestimation of hypoglycemia in infants must be considered if samples are not centrifuged or are not analyzed immediately after sampling. The extent of overestimation is more pronounced in samples with a high hematocrit, collected in capillary tubes. Cooling of samples does not prevent glucose consumption in vitro during the first 30 min. These results emphasize that, for glucose analysis, prompt handling of samples of newborns with a high hematocrit is necessary.

Which sample tube should be used for routine glucose determination?

BACKGROUND

Glucose is one of the most frequently requested analytes in clinical laboratory. Blood glucose analysis is affected from in vitro glycolysis. In order to determine the most suitable blood collection tube for this purpose we have compared different tubes: sodium fluoride, lithium heparin, sodium fluoride/citrate buffer containing tubes and serum with clot activator tube for the measurement of glucose when the tube has been kept at room temperature (RT) for up to 4h.

METHODS

Venous blood was collected from 49 healthy volunteers into Sarstedt S-Monovettes for glucose analysis. Reference plasma glucose was determined in a lithium heparin tube and immediately placed in an ice/water slurry. Within 10min it was centrifuged at 4°C and plasma was separated from the blood cells. Samples have been preserved at RT for 1, 2 and 4h after drawing. Glucose has been determined using a hexokinase method.

RESULTS

Glucose levels tested in a serum with clot activator tube, in lithium heparin and in sodium fluoride/sodium EDTA tubes when compared with lithium-heparin reference plasma did not meet the desirable bias for glucose (±1.8%) when kept at RT for up to 4h. GlucoEXACT tubes, when corrected by the Sarsted recommended factor of 1.16, showed a mean (95% CI) bias of +0.96% (0.45-1.47) at 1h, +1.40% (0.88-1.93) at 2h and +0.95% (0.44-1.46) at 4h, reaching the analytical goal for the desirable bias.

CONCLUSIONS

Samples collected into GlucoEXACT tubes containing sodium fluoride/citrate buffer liquid mixture are equivalent to those collected in reference plasma tubes avoiding glycolysis completely and within a 4h delay in plasma separation.

Effectiveness of citrate buffer-fluoride mixture in Terumo tubes as an inhibitor of in vitro glycolysis

Introduction

Glycolysis affects glucose determination in vitro. The placement of sample tubes in ice-water slurry with plasma separation within 30 minutes is recommended, or alternatively the use of a glycolysis inhibitor. The aim of our two-steps study was to evaluate which Terumo tube is best for glucose determination in routine clinical setting.

Materials and methods

In the first study, blood from 100 volunteers was collected into lithium heparin (LH), NaF/Na heparin (FH) and NaF/citrate buffer/Na₂EDTA (FC-Mixture) tubes. LH sample was treated as recommended and considered as reference, while FH and FC-Mixture samples were aliquoted, maintained at room temperature (RT) for 1, 2 and 4 hours; centrifuged and plasma analysed in triplicate. In the second study, samples from 375 volunteers were collected in LH, FH and FC-Mixture tubes and held at RT before centrifugation from 10 to 340 minutes, depending on each laboratory practice. Samples were analysed in one analytical run.

Results

In the first study, FH glucose concentrations were 5.15 ± 0.66 mmol/L, 5.05 ± 0.65 mmol/L and 5.00 ± 0.65 mmol/L (P < 0.001) in tubes stored at RT for 1, 2 and 4 hours, respectively. Mean biases in all time points exceeded the analytical goal for desirable bias based on biological variation criteria. FC-Mixture glucose concentrations were 5.48 ± 0.65 mmol/L, 5.46 ± 0.6 mmol/L and 5.46 ± 0.64 mmol/L in tubes stored at RT for 1, 2 and 4 hours, respectively. Mean biases for FC-Mixture glucose in all time points reached optimal analytical goals. In the second study, the biases for LH and FH glucose compared to reference FC-Mixture glucose exceeded the preset analytical goals, regardless of the blood collection to centrifugation time interval.

Conclusions

FC-mixture tubes glucose concentrations were preserved up to 4h storage at RT. We confirmed that NaF alone does not allow immediate glycolysis inhibition in real life pre-centrifugation storage conditions (up to 340 minutes). FC-Mixture should be used exclusively for glucose determination in laboratories unable to implement the recommended blood samples’ treatment.