Glycated haemoglobin and fasting plasma glucose tests in the screening of outpatients for diabetes and abnormal glucose regulation in Uganda: A diagnostic accuracy study

Background and objectives To understand the utility of glycated haemoglobin (HBA 1C ) in screening for diabetes and Abnormal Glucose Regulation (AGR) in primary care, we compared its performance to that of the fasting plasma glucose (FPG) test. Methods This was a prospective diagnostic accuracy study conducted in eastern Uganda. Patients eligible for inclusion were consecutive adults, 30–75 years, receiving care at the outpatient department of a general hospital in eastern Uganda. We determined the sensitivity, specificity and optimum cut-off points for HBA 1C and FPG tests using the oral glucose tolerance test (OGTT) as a clinical reference standard. Results A total of 1659 participants underwent FPG testing of whom 310 were also HBA 1C and OGTT tested. A total of 113 tested positive for diabetes and 168 for AGR on the OGTT. At recommended cut-off points for diabetes, the HBA 1C and FPG tests had comparable sensitivity [69.8% (95% CI 46.3–86.1) versus 62.6% (95% CI 41.5–79.8), respectively] and specificity [98.6% (95% CI 95.4–99.6) versus 99.4% (95% CI 98.9–99.7), respectively]. Similarly, the sensitivity of HBA 1C and the FPG tests for Abnormal Glucose Regulation (AGR) at ADA cut-offs were comparable [58.9% (95% CI 46.7–70.2) vs 47.7% (95% CI 37.3–58.4), respectively]; however, the HBA 1C test had lower specificity [70.7% (95% CI 65.1–75.8)] than the FPG test [93.5% (95% CI 88.6–96.4)]. At the optimum cut-offs points for diabetes [45.0 mmol/mol (6.3%) for HBA 1C and 6.4 mmol/L (115.2 mg/dl) for FPG], HBA 1C and FPG sensitivity [71.2% (95% CI 46.9–87.8) versus 72.7% (95% CI 49.5–87.8), respectively] and specificity [95.1% (95% CI91.8 97.2) versus 98.7% (95% CI 98.0 99.2), respectively] were comparable. Similarly, at the optimum cut-off points for AGR [42.0 mmol/mol (6.0%) for the HBA 1C and 5.5 mmol/l (99.0 mg/dl) for the FPG test], HBA 1C and FPG sensitivity [42.3% (95% CI 31.8–53.6) and 53.2 (95% CI 43.1–63.1), respectively] and specificity [89.1% (95% CI 84.1 92.7) and 92.7% (95% CI 91.0 94.1), respectively] were comparable. Discussion HBA 1C is a viable alternative diabetes screening and confirmatory test to the FPG test; however, the utility of both tests in screening for prediabetes in this outpatient population is limited.