Diagnostic Accuracy, Sensitivity and Specificity of Capillary POCT for Diagnosing Gestational Diabetes Mellitus

Background: The 75 g oral glucose tolerance test (OGTT) is the gold standard for diagnosing gestational diabetes mellitus (GDM) and, according to current guidelines, is recommended for postpartum testing. German guidelines recommend a two-step screening approach, which can delay treatment initiation. In order to prevent complications for mother and child, treatment of GDM should be started as early as possible. To expedite clinical decisions, point-of-care testing (POCT) is often used alongside venous laboratory analysis. For historical reasons, capillary blood was used for POCT at our competence center. This analysis evaluates the diagnostic accuracy of capillary POCT compared to the venous reference standard analyzed in our department of clinical chemistry. Methods: We retrospectively analyzed 401 OGTTs (260 during pregnancy, 141 postpartum) with simultaneous capillary POCT and venous laboratory glucose measurements and investigated the agreement between the two methods. Optimal capillary cut-offs were determined using ROC analysis. Results: In pregnant women (n = 260), capillary POCT showed 80.8% sensitivity and 73.4% specificity. Regarding the diagnostic classification, the initial agreement with the reference standard at fasting was 71.9% (8.9% false positives, 19.2% false negatives). Optimized capillary cut-offs—fasting ≥95 mg/dL (5.3 mmol/L), 1-h ≥203 mg/dL (11.3 mmol/L), and 2-h ≥174 mg/dL (9.7 mmol/L)—increased the proportion of correctly classified cases to 85.5% (fasting), 97.0% (1-h), and 94.4% (2-h), respectively, and effectively eliminated false negatives. Conclusions: While capillary POCT offers >80% sensitivity, its false-positive rate of more than 20% must be managed. Utilizing optimized cut-off values can mitigate this uncertainty. If at least one of these cut-offs is exceeded, capillary POCT via StatStrip® (Nova Biomedical Corporation, Waltham, MA, USA) provides a sufficient basis for treatment initiation.