OBJECTIVES: Fasting Plasma Glucose (FPG) and Hemoglobin A1c (HbA1c) are used as diagnostic tests for diagnosis of diabetes mellitus (DM) but it is unclear which test has the best diagnostic accuracy. This review aimed to estimate the diagnostic accuracy of HbA1c ≥ 6.5%, FPG ≥126 mg/dl, and the combination of HbA1c ≥ 6.5% or FPG ≥126 mg/dl, comparing with Oral Glucose Tolerance Test (2-hour post load glucose) (OGTT-2hr) ≥ 200 mg/dl for diagnosis DM.

METHODS: We performed a comprehensive search in PubMed, Embase, Cochrane Library, and Scopus from inception to September 24^th, 2021. Inclusion criteria is any study design comparing HbA1c ≥6.5%, FPG ≥126 mg/dl, and the combination of HbA1c ≥6.5% or FPG ≥126 mg/dl with OGTT 2hr ≥200mg/dl as the reference test. Data were independently extracted , while risk of bias were assessed using QUADAS-2 by two reviewers. Network meta-analysis was done using a bivariate regression model using Bayesian framework. Relative ranking of all tests were also assessed.

RESULTS: Out of 5,026 studies, 73 were included. The sensitivity of HbA1c, FPG, and combination of HbA1c and FPG was 0.51 (95%Credible Interval (CrI): 0.43, 0.58), 0.49 (0.43, 0.55), and 0.64 (95%CrI: 0.51, 0.75), while the specificity was 0.96 (0.94, 0.97), 0.98 (0.97,0.98), and 0.95 (0.88, 0.98), respectively. The diagnostic odds ratio (DOR) was also reported as 26.10 (15.75, 44.07), 41.86 (26.75, 64.62), 31.50 (12.24, 83.44), respectively. The corresponding positive likelihood ratio (LR+) was13.36 (8.91, 20.72), 21.94 (15.04, 31.88), and 11.78 (5.48, 26.56). In terms of ranking, the combination of HbA1c ≥6.5% or FPG ≥126 mg/dl is the best based on sensitivity whereas FPG ≥126 mg/dl is ranked the best based on LR+, specificity, and DOR.

CONCLUSIONS: Our findings suggest that FPG ≥126mg/dl should be recommended as the best diagnostic test for diabetes.