Reference interval for glycated hemoglobin (HbA1c) in non-pregnant, non-diabetic women in Ethiopia: a cross-sectional study

INTRODUCTION: glycated hemoglobin (HbA1c) serves as a key indicator of average blood glucose levels over the preceding 2-3 months, reflecting cumulative glucose exposure based on erythrocyte lifespan. Research has documented racial and ethnic disparities in the relationship between HbA1c levels and blood glucose. In this case, the non-Hispanic Black individuals consistently exhibit higher HbA1c levels than their non-Hispanic White and Hispanic counterparts. The primary objective of this study was to establish a country-specific reference interval for hemoglobin A1C in non-diabetic, non-pregnant women and to investigate the correlation between HbA1c levels and demographic and clinical characteristics. METHODS: an institution-based cross-sectional study was conducted on 129 non-pregnant, non-diabetic women aged ≥ 18 years in Addis Ababa, Ethiopia (December 4, 2024, to February 28, 2025); data were analyzed using IBM SPSS Statistics. Normality of continuous variables was assessed with Shapiro-Wilk and Kolmogorov-Smirnov tests. The reference interval for HbA1c was calculated parametrically (mean ± 2SD) if normally distributed or non-parametrically (2.5th- 97.5th percentiles) if not, other non-normal variables were summarized as median (range). Correlation between HbA1c and demographic or clinical characteristics was assessed using Pearson´s correlation coefficient. Outliers were identified and excluded using Tukey´s method. RESULTS: the HbA1c values, measured in mmol/mol, were normally distributed with a mean (±SD) of 38(±3.1), yielding a 95% reference interval of 32 - 44 mmol/mol. The corresponding DCCT percentage values ranged from 5.1% to 6.2%, with a mean (±SD) of 5.6% (±0.28). A statistically significant but weak positive correlation was observed between age and HbA1c levels (r =0.284, p = 0.007). CONCLUSION: this study found that the lower limit of the normal HbA1c reference interval in Ethiopian women was higher than reported in some previous studies. Age showed a modest influence on HbA1c levels, highlighting the importance of establishing population-specific reference intervals for accurate clinical interpretations.