Blood Glucose Determination: Effect of Tube Additives

Maintaining glucose integrity ex-vivo: Impact of preanalytical specimen handling

BACKGROUND

Adopting the WHO protocol for glucose analysis is arguably impractical in the routine clinical setting. Deviations may develop due to a lack of understanding regarding the impact of glycolysis on the accuracy of results.

AIM

We sought to assess the stability of glucose in two different blood collection tubes (BCT), BD Vacutainer® FX 'Fl-Ox' and Greiner Vacuette® FC-Mix 'FC-Mix' stored at room temperature (RT:18-22°C) and 4°C over 8.5 days.

METHOD

Each participant provided venous whole blood collected into 51 BCTs; 'Fl-Ox' (n = 26) and 'FC-Mix' (n = 25). One Fl-Ox sample from each participant was handled according to the WHO recommended method. The remaining BCTs were stored at 4°C/RT prior to analyses at designated study timepoints. Glucose was measured using the hexokinase assay on the Cobas® 8000 platform.

RESULTS

Participants (n = 8, Male = 2) were aged 24-56 years. Plasma glucose measured in FI-Ox BCTs according to the WHO sample-handling method had a median concentration of 5.73 mmol/L (Range: 5.39-10.37 mmol/L). Glucose decreased by greater than minimal difference (>0.26 mmol/L) in blood collected into Fl-Ox and stored @4°C/RT within 24 h of phlebotomy. FC-Mix BCT maintained glucose <0.26 mmol/L @4°C over a period of 8.5 days and up to 4 days @RT when compared to the WHO recommended method.

CONCLUSION

Glucose in FC-Mix BCT stored @4°C demonstrated the best agreement with results determined using the WHO specifications. When FC-Mix tubes were stored @RT, glucose was stable for 4 days. These findings suggest that the FC-Mix BCT effectively inhibits glycolysis and should be introduced into routine clinical practice.

Recommendation for the design of stability studies on clinical specimens

OBJECTIVES

Knowledge of the stability of analytes in clinical specimens is a prerequisite for proper transport and preservation of samples to avoid laboratory errors. The new version of ISO 15189:2022 and the European directive 2017/746 increase the requirements on this topic for manufacturers and laboratories. Within the project to generate a stability database of European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) Working Group Preanalytical Phase (WG-PRE), the need to standardise and improve the quality of published stability studies has been detected, being a manifest deficit the absence of international guidelines for the performance of stability studies on clinical specimens.

METHODS

These recommendations have been developed and summarised by consensus of the WG-PRE and are intended primarily to improve the quality of sample stability claims included in information for users provided by assay supplier companies, according to the requirements of the new European regulations and standards for accreditation.

RESULTS

This document provides general recommendations for the performance of stability studies, oriented to the estimation of instability equations in the usual working conditions, allowing flexible adaptation of the maximum permissible error specifications to obtain stability limits adapted to the intended use.

CONCLUSIONS

We present this recommendation based on the opinions of the EFLM WG-PRE group for the standardisation and improvement of stability studies, with the intention to improve the quality of the studies and the transferability of their results to laboratories.

Deviating glucose results in an international dual-center study. A root cause investigation

During a dual-center study on obese and normal weight children and adolescents, focusing on glucose metabolism, we observed a marked difference in glucose results (N = 16,840) between the two sites, Salzburg, Austria and Uppsala, Sweden (P < 0.001). After excluding differences in patient characteristics between the two populations as cause of this finding, we investigated other preanalytic influences. Finally, only the tubes used for blood collection at the two sites were left to evaluate. While the Vacuette FC-Mix tube (Greiner Bio-One, Kremsmünster, Austria) was used in Uppsala, in Salzburg blood collections were performed with a lithium heparin tube (LH-Monovette, Sarstedt, Germany). To prove our hypothesis, we collected two blood samples in either of these tubes from 51 children (Salzburg N = 27, Uppsala N = 24) and compared the measured glucose results. Indeed, we found the suspected bias and calculated a correction formula, which significantly diminished the differences of glucose results between the two sites (P = 0.023). Our finding is in line with those of other studies and although this issue should be widely known, we feel that it is widely neglected, especially when comparing glucose concentrations across Europe, using large databases without any information on preanalytic sample handling.

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".

The effect of drone transport on the stability of biochemical, coagulation and hematological parameters in healthy individuals

Objectives

Transport of blood tubes is mainly by car or pneumatic transport. The transportation of blood tubes by drones is a novel approach for rapid transportation of blood tubes over long distances. However, limited data on the stability of biochemical, coagulation and hematological parameters is available after transport of blood tubes by drone.

Methods

To investigate the effect of drone transport on the stability of blood parameters, four test flights were performed. Blood was drawn from 20 healthy individuals and 39 of the most frequently measured blood parameters were compared between 4 groups; immediate measurement (control), late measurement, transport by car and transport by drone. Total Allowable Error (TAE) of the EFLM Biological Variation Database was used to determine the clinical relevance of significant differences.

Results

The majority of blood parameters were not affected by drone transport. Eight of the measured parameters showed significant differences between all the groups; glucose, phosphate, potassium, chloride, hemoglobin, platelet count, APTT and Lactate dehydrogenase (LD). A clinically relevant increase for LD after transport and a decrease for glucose values in time and after transport compared with the control group was shown.

Conclusions

Transportation of blood tubes from healthy individuals by drones has a limited clinically relevant effect. From the 39 investigated blood parameters only LD and glucose showed a clinically relevant effect.

Different pre-analytical techniques and the results of 50 g oral glucose challenge tests

OBJECTIVE

We aimed to analyse the pre-analytical process and its effect of 50 g of oral glucose challenge test results for screening gestational diabetes mellitus.

RESEARCH DESIGN AND METHODS

The 50 g oral glucose challenge test was performed to 30 pregnant women, and the blood was collected as two samples for three tubes containing; serum separating jell (SSJ), sodium fluoride-potassium oxalate (NaF - KOx) and sodium citrate-containing tube. The first samples of the three tubes were centrifuged within 30 minutes, and second samples were centrifuged after 60 minutes and were analysed. One sample in SSJ tube and was analysed in the same day according to hospitals routine practice. The results were compared.

RESULTS

Among the 30 samples, the mean decrease in glucose levels was highest in the SSJ tube (0.38 mmol/L), followed by 0.16 mmol/L in Na citrate tube and 0.14 mmol/L in NaF-KOx tube. The hospital routine assessment with SSJ was 6.36 ± 1.90 mmol/L. The <30 and >60 minutes glucose results were 6.80 ± 1.88 mmol/L vs 6.42 ± 1.97 mmol/L for SSJ, 5.95 ± 1.60 mmol/L vs 5.78 ± 1.51 mmol/L for Na Citrate and 6.90 ± 1.86 mmol/L vs 6.75 ± 1.90 mmol/L for NaF-KOx mg/dL groups, respectively, and both the changes within time and the results between the tubes showed a statistically significant difference (P < .001).

CONCLUSION

In cases with longer assessment time and with different blood sample tubes, the clinician should also keep in mind that, especially with results under but close to the cut-off levels, an underdiagnosed gestational diabetes might be present.

Clot activators and anticoagulant additives for blood collection. A critical review on behalf of COLABIOCLI WG-PRE-LATAM

In the clinical laboratory, knowledge of and the correct use of clot activators and anticoagulant additives are critical to preserve and maintain samples in optimal conditions prior to analysis. In 2017, the Latin America Confederation of Clinical Biochemistry (COLABIOCLI) commissioned the Latin American Working Group for Preanalytical Phase (WG-PRE-LATAM) to study preanalytical variability and establish guidelines for preanalytical procedures to be applied by clinical laboratories and health care professionals. The aim of this critical review, on behalf of COLABIOCLI WG-PRE-LATAM, is to provide information to understand the mechanisms of the interactions and reactions that occur between blood and clot activators and anticoagulant additives inside evacuated tubes used for laboratory testing. Clot activators - glass, silica, kaolin, bentonite, and diatomaceous earth - work by surface dependent mechanism whereas extrinsic biomolecules - thrombin, snake venoms, ellagic acid, and thromboplastin - start in vitro coagulation when added to blood. Few manufacturers of evacuated tubes state the type and concentration of clot activators used in their products. With respect to anticoagulant additives, sodium citrate and oxalate complex free calcium and ethylenediaminetetraacetic acid chelates calcium. Heparin potentiates antithrombin and hirudin binds to active thrombin, inactivating the thrombin irreversibly. Blood collection tubes have improved continually over the years, from the glass tubes containing clot activators or anticoagulant additives that were prepared by laboratory personnel to the current standardized evacuated systems that permit more precise blood/additive ratios. Each clot activator and anticoagulant additive demonstrates specific functionality, and both manufacturers of tubes and laboratory professional strive to provide suitable interference-free sample matrices for laboratory testing. Both manufacturers of in vitro diagnostic devices and laboratory professionals need to understand all aspects of venous blood sampling so that they do not underestimate the impact of tube additives on laboratory testing.

Age and sex dependent reference intervals for random plasma/serum glucose concentrations related to different sampling devices and determined by an indirect procedure with data mining

The glucose concentration in plasma or serum is one of the most often requested analytical values in laboratory medicine. Whereas the analytical part of the glucose determination is well standardised, the standardisation of the pre-examination part (pre-analytical phase) is not sufficiently solved, yet. In view of the present controversial discussion regarding the most efficient prevention of pre-analytical glycolysis, the question arises whether the economical and logistic expenses for inhibiting glycolysis determining random glucose concentration are justified. In hospitals with adequate logistics (e.g. pneumatic tube systems for blood tubes) to guarantee a blood sample transport time of about 1 – 2 h, plasma or serum without prevention of glycolysis can be applied for random glucose concentrations if the reference limits are estimated by the laboratory. If such logistics are not available, especially in primary care services, either plasma or serum samples or whole blood in special tubes with anti-glycolytic additives may be sent to the laboratory.

A Prospective Evaluation of Point-of-Care Measurements of Maternal Glucose for the Diagnosis of Gestational Diabetes Mellitus

BACKGROUND

Point-of-care (POC) measurement of glucose is currently recommended only for the monitoring of gestational diabetes mellitus (GDM). This prospective observational study evaluated the use of POC measurements of maternal glucose to diagnose GDM in women being screened selectively with a 1-step 75 g oral glucose tolerance test (OGTT).

METHODS

The strictest preanalytic and analytic international laboratory standards were applied to measure maternal plasma glucose at fasting and at 1 and 2 h post glucose load. The recent International Association of Diabetes and Pregnancy Study Groups diagnostic criteria were used. At the same time, maternal capillary glucose was measured. Because of differences in plasma and capillary glucose measurements, regression analysis of POC capillary glucose results vs laboratory plasma glucose results was conducted. The regression equations for plasma glucose were derived in a derivation cohort (n = 102). These equations were applied in the validation cohort (n = 100). Predicted and actual plasma glucose values were compared.

RESULTS

Of the 202 women screened, 36.6% were nulliparous, 56.4% were obese, and 81.2% were Irish-born. Two thirds had a single risk factor for GDM, and a third had multiple risk factors. Based on the plasma measurements, 53.5% had GDM. As a predictor of GDM, the diagnostic accuracy of POC measurement was 83.0% (95% confidence interval, 74.2-89.8).

CONCLUSIONS

In high-resource settings where measures to inhibit glycolysis are implemented, the use of POC measurements for the diagnosis of GDM is not justified based on this study. In low- and medium-resource settings, where measures to inhibit glycolysis are not achievable, regression analysis using POC measurements may be acceptable compared with plasma samples subject to glycolysis.

Strict Preanalytical Oral Glucose Tolerance Test Blood Sample Handling Is Essential for Diagnosing Gestational Diabetes Mellitus

OBJECTIVE

Preanalytical processing of blood samples can affect plasma glucose measurement because ongoing glycolysis by cells prior to centrifugation can lower its concentration. In June 2017, ACT Pathology changed the processing of oral glucose tolerance test (OGTT) blood samples for pregnant women from a delayed to an early centrifugation protocol. The effect of this change on the rate of gestational diabetes mellitus (GDM) diagnosis was determined.

RESEARCH DESIGN AND METHODS

All pregnant women in the Australian Capital Territory (ACT) are recommended for GDM testing with a 75-g OGTT using the World Health Organization diagnostic criteria. From January 2015 to May 2017, OGTT samples were collected into sodium fluoride (NaF) tubes and kept at room temperature until completion of the test (delayed centrifugation). From June 2017 to October 2018, OGTT samples in NaF tubes were centrifuged within 10 min (early centrifugation).

RESULTS

A total of 7,509 women were tested with the delayed centrifugation protocol and 4,808 with the early centrifugation protocol. The mean glucose concentrations for the fasting, 1-h, and 2-h OGTT samples were, respectively, 0.24 mmol/L (5.4%), 0.34 mmol/L (4.9%), and 0.16 mmol/L (2.3%) higher using the early centrifugation protocol (P < 0.0001 for all), increasing the GDM diagnosis rate from 11.6% (n = 869/7,509) to 20.6% (n = 1,007/4,887).

CONCLUSIONS

The findings of this study highlight the critical importance of the preanalytical processing protocol of OGTT blood samples used for diagnosing GDM. Delay in centrifuging of blood collected into NaF tubes will result in substantially lower rates of diagnosis than if blood is centrifuged early.

Preanalytical issues related to routine and diagnostic glucose tests: Results from a survey in Spain

Introduction

Diabetes mellitus (DM) is one of the most prevalent diseases worldwide. The objective of this study was to find out under what preanalytical conditions routine and diagnostic glucose tests are performed across Spanish laboratories; and also what criteria are used for DM diagnosis.

Materials and methods

An online survey was performed by the Commission on Quality Assurance in the Extra-Analytical Phase of the Spanish Society of Laboratory Medicine (SEQC-ML). Access to the questionnaire was available on the home page of the SEQC-ML website during the period April-July 2018. Data analysis was conducted with the IBM SPSS^© Statistics (version 20.0) program.

Results

A total of 96 valid surveys were obtained. Most laboratories were in public ownership, serving hospital and primary care patients, with high and medium workloads, and a predominance of mixed routine-urgent glucose testing. Serum tubes were the most used for routine glucose analysis (92%) and DM diagnosis (54%); followed by lithium-heparin plasma tubes (62%), intended primarily for urgent glucose testing; point-of-care testing devices were used by 37%; and plasma tubes with a glycolysis inhibitor, mainly sodium fluoride, by 19%. Laboratories used the cut-off values and criteria recognized worldwide for DM diagnosis in adults and glucose-impaired tolerance, but diverged in terms of fasting plasma glucose and gestational DM criteria.

Conclusion

Preanalytical processing of routine and DM diagnostic glucose testing in Spain does not allow a significant, non-quantified influence of glycolysis on the results to be ruled out. Possible adverse consequences include a delay in diagnosis and possible under-treatment.

PREDICT: a checklist for preventing preanalytical diagnostic errors in clinical trials

Although the importance of guaranteeing a high level of preanalytical quality in routine diagnostic testing has already been largely acknowledged over the past decades, minor emphasis is currently being placed on the fact that accurate performance and standardization of many preanalytical activities are also necessary prerogatives of clinical trials. Reliable evidence exists that clear indications on how to manage the different preanalytical steps are currently lacking in many clinical trials protocols, nor have detailed authoritative documents been published or endorsed on this matter to the best of our knowledge. To fill this gap, the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) Working Group for Preanalytical Phase (WG-PRE) will provide here a specific checklist for preventing preanalytical diagnostic errors in clinical trials (PREDICT), especially focused on covering the most important preanalytical aspects of blood sample management in clinical studies, and thus encompassing test selection, patient preparation, sample collection, management and storage, sample transportation, as well as specimen retrieval before testing. The WG-PRE members sincerely hope that these recommendations will provide a useful contribution for increasing the success rate in clinical trials.

Effects of different tube types on patient classification using current diabetes decision limits

Management of diabetes is a challenge starting in the pre-analytical phase with selecting the most appropriate glycolysis inhibitor. Study goal was to calculate the impact of tubes with different glycolysis inhibitors on the classification of the glycemic control of 157,415 consecutive hospital patients according to current WHO diabetes criteria.

Methods

Glucose and lactate were measured in parallel in samples from 68 healthy subjects collected and stored in different sample tubes from Sarstedt and Greiner. Bias to baseline conditions (fluoride heparin (FH) tubes, centrifugation within 1 h) was determined.

Results

In baseline samples, glucose concentration in fluoride/EDTA/citrate (FC) plasma was ~13% higher and lactate concentration ~20% lower compared to FH, fluoride oxalate, and fluoride EDTA plasma, and in serum. Glucose recovery after storage up to 48 h was 99–101% in the different tubes, but the effectiveness of glycolysis inhibition by FC was inconsistent. Based on the observed mean bias of 12% when FC tubes are used, we estimate an increase of 48.4–55.8% in the frequency of patients with impaired glucose levels using current WHO criteria.

Conclusion

Using current established decision limits, the number of patients with impaired glucose levels in the hospital would increase substantially with a strong impact on patient treatment and consumption of resources. The unpredictable failure of glycolysis inhibition in FC tubes does not allow to adjust the decision limits by a fixed factor. In the absence of prospective outcome studies with FC tubes, we recommend to measure glucose in samples containing FH.

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Fluoride citrate EDTA (FC) fails to inhibit glycolysis consistently.

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Glucose testing from FC tubes introduces a positive mean bias of ~0.5 mmol/L (12%) at the decision limit.

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Fluoride EDTA/heparin or Fluoride oxalate tubes should be preferred for glucose and lactate measurement.

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Use of FC tubes increases the frequency of impaired fasting glucose and diabetes by ~50% using current decision limits.

Impact of blood cell counts and volumes on glucose concentration in uncentrifuged serum and lithium-heparin blood tubes

BACKGROUND

Although it is known that glucose concentration exhibits a time-dependent decay in uncentrifuged serum and lithium-heparin blood tubes, no evidence exists on how this variation may depend on blood cell counts (CBC) and volumes.

METHODS

Venous blood was drawn from 30 non fasting healthy volunteers into three serum and three lithium-heparin tubes. One serum and lithium-heparin tubes were centrifuged within 15 min after collection and glucose was measured with a hexokinase assay. The second and third serum and lithium-heparin tubes were maintained at room temperature for 1 and 2 h after the first tubes were centrifuged. These other tubes were then centrifuged and glucose was measured. CBC was performed in the first lithium-heparin tube, before centrifugation.

RESULTS

The mean decrease of glucose was higher in lithium-heparin plasma than in serum (0.33 vs. 0.24 mmol/L/h; p<0.001). Glucose concentration decreased by 7% and 5% per hour in lithium-heparin plasma and serum, respectively. In univariate analysis, the absolute decrease of glucose concentration was associated with sex (higher in men than in women), red blood cell (RBC) count, hematocrit, white blood cell (WBC) count, neutrophils and monocytes in both lithium-heparin plasma and serum. In multivariate analysis, the decrease of glucose concentration remained independently associated with RBC, WBC, neutrophils and monocytes in both sample matrices. No significant association was found with platelet number and erythrocyte or platelet volume.

CONCLUSIONS

Glucose concentration decrease in uncentrifuged lithium-heparin and serum tubes depends on the baseline number of RBC, WBC, neutrophils and monocytes within the tubes.

Leukocytosis interference in clinical chemistry: Shall we still interpret test results without hematological data?

Background

Extreme leukocytosis is known to induce remarkable variations of some clinical chemistry tests, thus leading to possible clinical misinterpretation. This study aimed to define whether also moderate leukocytosis may influence the stability of glucose and blood gases.

Methods

Blood samples are sent to the local laboratory through a pneumatic tube system. Clinical chemistry testing is routinely performed using Lithium-heparin tubes (for glucose) and heparin blood gases syringes (for blood gas analysis). Stability of glucose (in uncentrifuged blood tubes) and blood gases (in syringes) was hence evaluated in samples maintained at room temperature. Results were also analyzed in 2 subgroups of samples with different leukocyte counts, i.e., those with leukocytes <15 × 10⁹/L and those with leukocytes >15 × 10⁹/L.

Results

An accelerated decrease of pH was observed in blood gases syringes with leukocytosis (i.e., >15 × 10⁹/L), while no difference was noted for other blood gases parameters (PCO2, PO2). Spurious and time-dependent hypoglycemia was noted in uncentrifuged blood tubes of patients with leukocytosis.

Conclusions

The results of our study suggest that even modest leukocytosis (i.e., around 15 × 10⁹/L), which is frequently encountered in clinical and laboratory practice, may be associated with significant variations of both glucose and pH. This would lead us to conclude that results of these parameters shall be accompanied by those of hematologic testing to prevent clinical misinterpretation, namely with leukocyte counts.