Standard procedure for OGTT and blood collection:
Our standard procedure for OGTT in pregnancy was followed. Women were instructed to fast from 10 pm the night before the test (water was allowed). Trained staff in the antenatal department carried out the OGTT. At 0-minute (fasting) and 120-minutes post 75-gram glucose load, VPG samples were collected by venepuncture into sodium fluoride oxalate (BD Vacutainer®) tubes and sent to the laboratory. For POC- StatStrip®, capillary whole blood was obtained from finger prick or earlobe prick.
Glucose analysis :
VPG was measured in the main hospital laboratory using Roche (Cobas 8000 c702, Burgess Hill, UK) chemistry analyser. It employs the enzymatic hexokinase method. The laboratory (Synnovis) is accredited by the United Kingdom Accreditation Service (UKAS) for the international medical laboratory standard ISO15189.
POC-CBG was measured using Nova StatStrip® Glucose Hospital Meter which uses a modified glucose oxidase method. The StatStrip® Internal Quality Control (IQC) was performed daily with level 1 and level 3 Nova StatStrip® control solution, according to our standard practice. The External Quality Control (EQC) of the meter was performed bimonthly by WEQAS (the largest provider of External Quality Assessment services for POC tests in the UK).
OGTT interpretation :
NICE (2015) criteria for diagnosis of GDM were used: fasting glucose concentration ≥ 5.6 mmol/L or 2-hour post-75g oral glucose load glucose concentration ≥7.8 mmol/L.
Statistical Analysis :
Data were analysed using Analyse-It (version 5.40.2) and are reported as median and inter-quartile range (IQR). Pearson correlation, Bland Altman plot and Passing Bablok regression analysis were used to assess the agreement between the two methods. A p value of <0.05 was considered statistically significant. Results are presented for all data and for fasting and 2-hour concentrations. For each time-point, concordance in meeting GDM diagnostic threshold, sensitivity, specificity, false positive (FP) rate, false negative (FN) rate, positive predictive value (PPV) and negative predictive value (NPV) were calculated. Receiver Operating Characteristic curve (ROC) was used to compare the diagnostic sensitivity and specificity. Sub-analysis was performed to compare fasting POC-StatStrip® concentrations ≤5mmol/l and 2-hour <7.5mmol/l or >9.5mmol/l with the corresponding Lab-VPG concentrations.