Time is glucose, can't miss gestational diabetes

Gestational diabetes mellitus (GDM) is associated with adverse perinatal outcomes, if not treated. International guidelines recommend screening "all or high-risk women" at the initial prenatal visit, when a fasting plasma glucose (FPG) between 92 and 126 mg/dL is diagnostic for GDM. However, glucose testing may be affected by a great pre-analytical variability (usually overlooked), due to, for example, kind of sample (serum/plasma), temperature of storage, time between blood draw and centrifugation (in-tube glycolysis), and use of a glycolysis inhibitor. So GDM may be easily missed. We aimed to evaluate the potential characteristics of this important issue.

FPG was tested by both "routine" and "gold standard" protocols in 60 women at the first trimester of gestation, presenting for GDM screening. "Routine" blood plasma was collected in a tube with sodium fluoride, kept at room temperature, centrifuged, and tested 30-45 min after blood draw. "Gold standard" was a specimen from the same blood sample that was centrifuged within 5 min and tested together with the "routine" specimen.

In the "routine" protocol, 10 mg/dL on average was lost for each determination. Thirteen cases of GDM and two of overt diabetes (FPG >126 mg/dL) were missed in this preliminary series.

The risk for GDM underdiagnosis in the first half of pregnancy appears to be actual and wide. A closer collaboration between clinicians and pathologists is critical, allowing a stricter adherence to the laboratory guidelines to be ensured.