Pregnancy diabetes: A comparison of diagnostic protocols based on point-of-care, routine and optimized laboratory conditions

Clinical utility of point-of-care glucose testing in the assessment of gestational diabetes: Prospective cohort study

OBJECTIVE

To assess the clinical utility of point-of-care (POC) capillary blood glucose (CBG) testing in the assessment of gestational diabetes mellitus (GDM) during oral glucose tolerance test (OGTT).

DESIGN

Prospective cohort study.

SETTING

Antenatal clinics at King's College Hospital.

POPULATION

Women screened for GDM between March and June 2020.

METHODS

The CBG was measured using the POC StatStrip® test and the venous plasma glucose (VPG) was measured by Roche analyser (Cobas 8000 c702). GDM was diagnosed based on the 2015 National Institute for Health and Clinical Excellence (NICE) Clinical Guideline criteria. The two methods were compared statistically using Analyse-It 5.40.2.

MAIN OUTCOME MEASURES

Diagnostic sensitivity, specificity, positive and negative predictive values (PPV and NPV) for the POC StatStrip® test, compared with VPG measured by reference laboratory method.

RESULTS

A total of 230 women were included. The number and percentage of women with glucose concentrations above the GDM threshold using the POC StatStrip® test versus laboratory VPG measurement was 15 (6.5%) versus eight (3.4%) at fasting and 105 (45.6%) versus 72 (31.1%) at 2 h, respectively. The sensitivity and specificity values (and 95% CIs) for the POC StatStrip® test were 88% (52%-99%) and 97% (93%-98%) at fasting and 97% (91%-99%) and 79% (71%-84%) at 2 h, respectively. However, the specificity and the NPV for the POC StatStrip® test for concentrations of ≤5.0 mmol/L at fasting or <7.5 mmol/L at 2 h were 100%, and the sensitivity and the PPV for concentrations of >9.5 mmol/L at 2 h were 100%.

CONCLUSIONS

In our cohort the POC measurement of CBG cannot entirely replace the laboratory method for the OGTT; however, it can be used to rule out/rule in GDM for glucose concentrations of ≤5.0 mmol/L at fasting or <7.5/>9.5 mmol/L at 2 h.

Prevalence estimates of diabetes in pregnancy in a rural, sub-Saharan population

AIMS

To determine the prevalence of Hyperglycaemia first Detected in Pregnancy (HDIP) in a cohort of women from rural Gambia and compare the diagnostic ability of capillary blood glucose (CBG) sampling to identify HIP versus laboratory-based analysis of venous plasma glucose (VPG).

METHODS

Pregnant women from rural Gambia (N = 251) underwent a 75 g Oral Glucose Tolerance Test (OGTT) at 28-weeks of gestation. Gestational Diabetes Mellitus was assessed as fasting glucose concentration ≥ 5.1-6.9 mmol/L; ≥10.0 mmol/L at 1-h post load; or ≥ 8.5 mmol/L at 2-h post load and Diabetes in Pregnancy as fasting glucose > 7.0 mmol/L.

RESULTS

A total of 199 and 244 women had VPG and CBG measurements respectively, and 198 women had both. 32 women (16.1%) were diagnosed with HDIP using VPG, mostly based on fasting concentrations.

CONCLUSIONS

The prevalence of HDIP in rural Gambia was higher than anticipated, emphasising a need for maternal diabetic policy. Based on the current findings, tailored recommendations could include measuring fasting VPG alone when conducting a full OGTT is not feasible. Similarly, CBG may be of value for excluding disease and thereby limiting costly laboratory-based investigations to a select few.

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.

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.

Accuracy of five plasma calibrated glucometers to screen for and diagnose gestational diabetes mellitus in a low resource clinic setting

AIMS

We investigated the clinical and analytic accuracy of five plasma calibrated glucometers, the use of which is advocated by the World Health Organisation and the International Federation of Gynaecology and Obstetrics, to screen for and diagnose gestational diabetes mellitus (GDM) in low resource settings.

METHODS

592 consecutive black African women underwent a 75 g oral glucose tolerance test (OGTT) at 24-28 weeks gestation at an urban South African community health clinic. Capillary glucose was measured by one of five glucometer brands, each paired with a routine laboratory hexokinase method of plasma glucose measurement. The laboratory results served as the gold standard reference test for GDM diagnosis. World Health Organisation GDM diagnostic thresholds were applied to glucometer and laboratory results.

RESULTS

Glucometer and laboratory determined GDM prevalence was 75/592 (12.7%) and 30/592 (5.1%) with an elevated fasting glucose diagnostic in 64/75 (85%) and 24/30 (80%) of cases respectively. The proportion of glucometer results fulfilling ISO 15197:2013 recommended analytic accuracy at fasting, 60, and 120 min of the OGTT was 92.4%, 49.8% and 61.5%, with Bland Altman method revealing a positive glucometer bias of 0.22 mmol/l (-0.69-1.12 mmol/l), 0.96 mmol/l (-0.65-2.56 mmol/l) and 0.73 mmol/l (-0.73-2.19 mmol/l) respectively. Only three of the glucometer brands evaluated fulfilled ISO 15197:2013 analytic accuracy requirements and this was only achieved at fasting. All glucometers tested were inaccurate at one and two hours of the OGTT.

CONCLUSIONS

Not all glucometers may be suitable for GDM screening as only three were accurate compared to the reference test and then only at fasting of the OGTT. Importantly, laboratory fasting glucose was diagnostic of GDM in 80% of cases in this study population.

The impact of differences in plasma glucose between glucose oxidase and hexokinase methods on estimated gestational diabetes mellitus prevalence

We evaluated the extent of measurement discordance between glucose oxidase and hexokinase laboratory methods and the effect of this on estimated gestational diabetes mellitus (GDM) prevalence in a routine clinical setting. 592 consecutive urban African women were screened for GDM. Paired venous specimens were submitted to two independent calibrated laboratories that used either method to measure plasma glucose concentrations. World Health Organisation diagnostic criteria were applied. GDM prevalence determined by the glucose oxidase and hexokinase methods was 6.9% and 5.1% respectively. The overall GDM prevalence was 9%. Only 34% of GDM positive diagnoses were common to both laboratory methods. Bland Altman plots identified a bias of 0.2 mmol/l between laboratory methods. Plasma glucose concentrations measured by the glucose oxidase method were more platykurtic in distribution. Low diagnostic agreement between laboratory methods was further indicated by a Cohen's kappa of 0.48 (p < 0.001). Reports of GDM prevalence using either the glucose oxidase or hexokinase laboratory methods may not be truly interchangeable or directly comparable.

Glucose meters: What’s the laboratory reference glucose?

Background

The accuracy of glucose meters is evaluated by comparing their results with those from a reference laboratory glucose analyser. The main scientific societies recommend the use of a prompt glycolysis inhibitor such as citrate for an accurate glucose determination. In the present preliminary study, we discuss the bias between capillary and plasma glucose measured concentrations, determined in two Italian clinical laboratories, using tubes containing an NaF and citrate mixture in liquid and granular form.

Methods

139 volunteers in whom 75 g OGTT was requested were recruited. Basal capillary glucose was determined using Abbott FreeStyle Precision Neo in Brescia (n=63), while clinical laboratory reference P-glucose was determined using tubes containing NaF/K3EDTA and liquid NaF/Na2EDTA/citrate. Basal capillary glucose was determined using a Roche Cobas Accu-Chek Inform II in Vicenza (n=76), while P-glucose was determined using tubes containing NaF/K2Ox and NaF/Na2EDTA/citrate in granulated form. Reference P-glucose was determined with a hexokinase method on Dimension Vista systems. Differences between capillary and reference P-glucose were evaluated according to ADA/ISO 15197:2013 specifications.

Results

96.82% and 97.37% of capillary determinations were within specifications when liquid and granular citrate mixture tubes were used, respectively. Conversely, only 73.02% and 80.26% of determinations were within criteria using NaF.

Conclusions

It’s important to know what is the laboratory reference glucose in evaluating glucose meters’ accuracy. The evaluation of glucometers’ accuracy with respect to a reference laboratory may be wrong if tubes containing only NaF are used due to in vitro glycolysis. Only tubes containing citrate mixture permit the correct evaluation of glucose meters’ accuracy.

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.

Technical and clinical validation of the Greiner FC-Mix glycaemia tube

BACKGROUND

Measurement of adequate glucose concentrations is complicated by in vitro breakdown of glucose due to glycolysis. Unlike the commonly used NaF-EDTA and NaF-oxalate phlebotomy tubes, citrated NaF-EDTA tubes are reported to directly and thereby completely inhibit glycolysis. Recently, Greiner introduced the Vacuette® FC-Mix NaF-EDTA-citrate tube, currently the only NaF-citrate tube without volume-disturbing liquid additions available on the European market. Here we present its potential as alternative for the laborious and therefore unfeasible conditions for glucose sampling as recommended by the World Health Organization (WHO).

METHODS

The FC-Mix tube was tested against the WHO recommended method of optimal laboratory conditions, both in healthy volunteers and pregnant woman undergoing oral glucose tolerance test (oGTT) for screening of gestational diabetes mellitus (GDM). Glucose concentrations were measured after different incubation times (0-48 h) and temperatures (room temperature, 37 °C), both in uncentrifuged whole blood and centrifuged material.

RESULTS

Deming regression analysis shows that glucose concentrations measured in the FC-Mix tube correlate to the WHO recommended method. Stability is maintained at room temperature for 48 h and at least 24 h at 37 °C. The use of the FC-Mix tube was also validated in screening for GDM and proved comparable to the WHO recommended method in diagnostic outcome.

CONCLUSIONS

The new Greiner FC-Mix tube combines the easy handling of a routine tube with dry additive with the ability to immediately inhibit glycolysis as in the WHO method for optimal pre-analytical and analytical conditions and performs equally to those conditions when screening for GDM.