The 1-hour post-load glucose level is more effective than HbA1c for screening dysglycemia
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To assess the performance of HbA1c and the 1-h plasma glucose (PG ≥ 155 mg/dl; 8.6 mmol/l) in identifying dysglycemia based on the oral glucose tolerance test (OGTT) from a real-world clinical care setting.
This was a diagnostic test accuracy study. For this analysis, we tested the HbA1c diagnostic criteria advocated by the American Diabetes Association (ADA 5.7–6.4 %) and International Expert Committee (IEC 6.0–6.4 %) against conventional OGTT criteria. We also tested the utility of 1-h PG ≥ mg/dl; 8.6 mmol/l. Prediabetes was defined according to ADA-OGTT guidelines. Spearman correlation tests were used to determine the relationships between HbA1c, 1-h PG with fasting, 2-h PG and indices of insulin sensitivity and β-cell function. The levels of agreement between diagnostic methods were ascertained using Cohen’s kappa coefficient (Κ). Receiver operating characteristic (ROC) curve was used to analyze the performance of the HbA1c and 1-h PG test in identifying prediabetes considering OGTT as reference diagnostic criteria. The diagnostic properties of different HbA1c thresholds were contrasted by determining sensitivity, specificity and likelihood ratios (LR).
Of the 212 high-risk individuals, 70 (33 %) were identified with prediabetes, and 1-h PG showed a stronger association with 2-h PG, insulin sensitivity index, and β-cell function than HbA1c (P < 0.05). Furthermore, the level of agreement between 1-h PG ≥ 155 mg/dl (8.6 mmol/l) and the OGTT (Κ[95 % CI]: 0.40[0.28–0.53]) diagnostic test was stronger than that of ADA-HbA1c criteria 0.1[0.03–0.16] and IEC criteria (0.17[0.04–0.30]). The ROC (AUC[95 % CI]) for HbA1c and 1-h PG were 0.65[0.57–0.73] and 0.79[0.72–0.85], respectively. Importantly, 1-h PG ≥ 155 mg/dl (8.6 mmol/l) showed good sensitivity (74.3 % [62.4–84.0]) and specificity 69.7 % [61.5–77.1]) with a LR of 2.45. The ability of 1-h PG to discriminate prediabetes was better than that of HbA1c (∆AUC: −0.14; Z value: 2.5683; P = 0.01022).
In a real-world clinical practice setting, the 1-h PG ≥ 155 mg/dl (8.6 mmol/l) is superior for detecting high-risk individuals compared with HbA1c. Furthermore, HbA1c is a less precise correlate of insulin sensitivity and β-cell function than the 1-h PG and correlates poorly with the 2-h PG during the OGTT.
KeywordsHbA1c OGTT Dysglycemia Prediabetes 1-hour post-load glucose Diabetes prevention
This study was funded by CTSI Grant Number 1UL1RR029893 (NCRR, NIH, and the Schuman Foundation) and partly by NIH-K24-NR012226.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
This study was approved by the New York University School of Medicine Institutional Review Board.
Human and animal rights disclosure
All human rights were observed in keeping with Declaration of Helsinki 2008 (ICH GCP). There are no animal rights issues as this is a clinical study.
Informed consent was obtained from all individual participants included in the study.
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