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.