AimsGestational diabetes mellitus (GDM) is a prevalent and potentially serious condition which may put both mothers and neonates at risk. The current recommendation for diagnosis is the oral glucose tolerance test (OGTT). This study aimed to determine the usefulness of HbA1c test as a diagnostic tool for GDM as compared to the traditional criteria based on the OGTT.MethodsThis was a diagnostic test accuracy study. We performed OGTT and HbA1c test in women attending prenatal visits at a tertiary hospital. GDM was defined according to WHO1999 or ADA/WHO 2013 criteria. ROC curve was used to evaluate the diagnostic performance of HbA1c. Sensitivity, specificity and likelihood ratios for different HbA1c cut-off points were calculated.ResultsOf the 262 women in the third trimester of gestation enrolled in the study, 86 (33%) were diagnosed with GDM. Only five of these women presented HbA1c ≥48 mmol/mol (6.5%). This cut-off point presented 100% specificity but very low sensitivity (7%). Based on ROC curve, and considering OGTT as the reference criterion, HbA1c ≥40 mmol/mol (5.8%) showed adequate specificity in diagnosing GDM (94.9%) but low sensitivity (26.4%). Unlike, HbA1c values of 31 mmol/mol (5.0%) presented adequate sensitivity (89.7%) but low specificity (32.6%) to detect GDM. For women with HbA1c ≥40 mmol/mol (5.8%), the positive and negative likelihood ratios were 5.14 (95%CI 2.49–10.63) and 0.78 (0.68–0.88), respectively. The post-test probability of GDM was about 40%, representing a 4.0-fold increase in the mean pre-test probability. This cut-off point could eliminate the need for the unpleasant and laborious OGTT tests in almost one third of cases, as 38% of patients with GDM may be diagnosable by HbA1c test alone.ConclusionsOur results show that combined HbA1c and OGTT measurements may be useful in diagnosing GDM.

HbA(1c) ≥ 6.5% (48 mmol/mol) showed limited sensitivity to diabetes diagnosis, although with high specificity. The results suggest that this cut-off point would not be enough to diagnose diabetes. Its use as the sole diabetes diagnostic test should be interpreted with caution to assure the correct classification of diabetic individuals.

Background We conducted a systematic review and meta-analysis to establish the overall accuracy of glycated hemoglobin (HbA1c) in the diagnosis of gestational diabetes mellitus (GDM) diagnosis. Methods We searched MEDLINE, EMBASE, SCOPUS and ClinicalTrials.gov up to October 2018, using keywords related to GDM, HbA1c and diagnosis. Studies were included that were carried out with pregnant women without previous diabetes that assessed the performance of HbA1c (index test) compared to the 75 g oral glucose tolerance test (OGTT) (reference test) for the diagnosis of GDM, that measured HbA1c by standardized methods and presented data necessary for drawing 2 × 2 tables. Results This meta-analysis included eight studies, totaling 6406 pregnant women, of those 1044 had GDM. The diagnostic accuracy of HbA1c was reported at different thresholds ranging from 5.4% (36 mmol/mol) to 6.0% (42 mmol/mol), and the area under the curve (AUC) was 0.825 (95% confidence interval [CI] 0.751–0.899), indicating a good level of overall accuracy. The pooled sensitivities and specificities were 50.3% (95% CI 24.8%–75.7%) and 83.7% (67.5%–92.7%); 24.7% (10.3%–48.5%) and 95.5% (85.7%–98.7%); 10.8% (5.7%–19.41%) and 98.7% (96.2%–99.5%); 12.9% (5.5%–27.5%) and 98.7% (97.6%–99.3%), for the cut-offs of 5.4% (36 mmol/mol), 5.7% (39 mmol/mol), 5.8% (40 mmol/mol) and 6.0% (42 mmol/mol), respectively. Conclusions We observed a high heterogeneity among the studies. The effect of ethnicities, different criteria for OGTT interpretation and the individual performance of HbA1c methods may have contributed to this heterogeneity. The HbA1c test presents high specificity but low sensitivity regardless of the threshold used to diagnose GDM. These findings point to the usefulness of HbA1c as a rule-in test. HbA1c should be used in association with other standard diagnostic tests for GDM diagnosis.

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