Comparison of 100-g Oral Glucose Tolerance Test Using Venous Plasma and Capillary Blood for Screening Gestational Diabetes Mellitus

Abstract

The 100-g oral glucose tolerance test (OGTT) for diagnosing gestational diabetes mellitus (GDM) typically uses venous plasma and takes around six hours. Switching to using capillary blood from finger pricks could potentially reduce waiting times and avoid the difficulties associated with drawing venous blood. This research involved 333 pregnant women attending antenatal care at Ang Thong Hospital who had screened positive on the 50-g glucose challenge test (GCT). The study compared fasting and post-ingestion blood glucose levels at 1, 2, and 3 hours using both capillary and venous blood samples. Results showed a significant correlation between the two methods, with Pearson correlation coefficients of 0.811, 0.852, 0.870, and 0.862 for fasting and at 1, 2, and 3 hours post-ingestion, respectively (p<0.001). However, it was noted that capillary blood glucose levels were consistently higher than those obtained from venous plasma. The diagnosis rate of GDM was notably higher using capillary blood, with 47.4% of participants diagnosed compared to 29.1% using the standard venous plasma method. The sensitivity and specificity of capillary blood testing were 95.9% and 72.5%, respectively. In conclusion, while the 100-g OGTT using capillary blood can be a viable initial screening alternative, especially in settings where venipuncture is challenging or resources are limited, it should not replace the standard method. Due to the higher glucose readings and potential discrepancies, confirmatory testing with venous plasma remains crucial for accurate diagnosis of gestational diabetes.