Purpose Results from a few studies have been conflicting as to whether iron deficiency alters HbA1c reliability and the mechanisms on how iron might affect HbA1c reliability are not fully known. We aimed to compare the relationship between HbA1c and mean glucose concentrations measured by continuous glucose monitoring in iron replete and iron deplete states among non-anaemic type 2 diabetes mellitus (T2DM) patients.

Methods We compared the differences in HbA1c between iron replete and deplete groups using the Chi-square test for categorical data and the Mann-Whitney U test for continuous data. We also evaluated the correlation between HbA1c and mean plasma glucose for both iron-replete and iron-deplete individuals using Pearson’s correlation and linear regression.

Results A total of 146 of the 213 participants screened had complete data and were considered for final analysis. 43/146 (29.5%) had iron deficiency and 103 were iron replete. No significant difference was observed in HbA1c levels between iron-replete and iron-deplete individuals: 69 [51.0, 85.0] vs 62 [46.0, 83.0] mmol/mol, P 0.291). There was a strong positive correlation between HbA1c and mean plasma glucose concentration for both iron-replete and iron-deplete individuals (Pearson Correlation coefficient: 0.83 (0.76 – 0.91) and 0.93 (0.89 – 0.98), respectively).

Conclusions HbA1c correlates well with mean blood glucose even in the iron deplete state amongst non-anaemic T2DM individuals. However, larger studies are needed to confirm these findings, particularly at screening and diagnostic thresholds.

The authors have declared no competing interest.

Funding for the study was received from the National Institute of Health Research (UK) award reference 17/63/131: NIHR Global Health Research Group at the University of Exeter: Improving outcomes in sub-Saharan African diabetes through better diagnosis and treatment. MJN and AJN received the award. The sponsors did not play any role in the study design, data collection and analysis, decision to publish and preparation of the manuscript. https://www.nihr.ac.uk

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