HbA1c level decreases in iron deficiency anemia



Hemoglobin A1c (HbA1c) is the major form of glycosylated hemoglobin. There are conflicting data on changes in HbA1c levels in patients with iron deficiency anemia (IDA). The present study aimed to investigate the effects of HbA1c levels in the presence of IDA, the effects of iron treatment on HbA1c levels, as well as the relationship between the severity of anemia and HbA1c levels in patients without diabetes.

Design and methods

A total of 263 patients without diabetes mellitus (DM) who were admitted to Cukurova University, Faculty of Medicine, Department of Endocrinology and Hematology or who were followed up in this clinic and diagnosed as having IDA were included in the study. A total of 131 patients had IDA. The control group comprised 132 age-matched and sex-matched healthy individuals.


The mean HbA1c level was significantly lower in the group with IDA (5.4%) than in the healthy control group (5.9%; p < 0.05). When the patients were divided into three groups according to the severity of anemia through Hb levels, HbA1c levels were observed to decrease as the severity of the anemia increased (5.5%, 5.4%, and 5%, respectively; p > 0.05). The HbA1c levels of the patients with IDA were higher after iron therapy (from 5.4 ± 0.5 to 5.5 ± 0.3; p = 0.057). The mean hemoglobin (Hb), hematocrit (Hct), mean cell volume (MCV), mean corpusculer hemoglobin (MCH), and ferritin values also increased after iron therapy (p < 0.05).


The study results showed that IDA was associated with low HbA1c levels, and increased after iron therapy. Based on the study findings, it is necessary to consider the possible effects of IDA on HbA1c levels.


Hemoglobin A1c (HbA1c) is the most dominant fraction of HbA1 and is formed by the glycation of the valine amino acid in the β‑chain of hemoglobin [1]. It reflects blood glucose levels over the past 3 months and has been used in diagnosis of diabetes mellitus (DM) for some time already according to ADA/EASD guidelines. Also, HbA1c levels have a positive correlation with hyperglycemia and its duration [2]. The HbA1c formation used to assess glycemic status in clinical practice depends on several factors, such as the release of HbA1c in reticulocytes from bone marrow, the synthesis rate of HbA1c (or Hb glycosylation rate), and the mean age of circulating erythrocytes [3,4,5]. Detectable HbA1c levels are affected by plasma glucose levels, the measurement method used, the presence of variant hemoglobin affecting erythrocyte recovery, hemolytic anemia, nutritional anemia, thalassemia, uremia, pregnancy, and acute and chronic hemorrhage.

Anemia is a very common problem worldwide. According to the World Health Organization, iron deficiency anemia (IDA) is the most common nutritional deficiency [6,7,8,9]. Iron deficiency is still the most common cause of anemia in Turkey [10]. Although IDA is very common, study results on the effect of IDA on HbA1c are still controversial. In several studies that compared HbA1c levels before and after iron therapy in patients with IDA but without diabetes, HbA1c levels were found to be higher before treatment, and a significant decrease was observed after treatment [11,12,13,14]. In addition, patients with IDA without diabetes and a healthy control group had the same HbA1c levels in some studies [15, 16].

The underlying mechanisms and modes of action of HbA1c levels in patients with IDA and anemia but without diabetes are still controversial. The present study aimed to investigate the changes in HbA1c levels in patients without diabetes who had IDA due to the importance of HbA1c in the diagnosis and follow-up of DM, and due to the frequency of IDA as a clinical finding.

Material and methods

Study population

A total of 263 individuals consisting of 131 patients (116 women, 15 men, mean age 39 ± 10 years) who were diagnosed as having IDA and 132 healthy individuals (118 women, 14 men, mean age 41 ± 9 years) who were admitted to Cukurova University, Faculty of Medicine, Department of Endocrinology and Hematology were included in the study. The control group consisted of age-matched and sex-matched individuals. Those who had impaired fasting glucose, DM, hemoglobinopathy, hemolytic anemia, chronic alcohol use, chronic renal failure, chronic liver failure, pregnancy, and breastfeeding history were excluded. Hemoglobin, hematocrit, mean cell volume (MCV), ferritin, insulin, fasting blood glucose, and HbA1c were measured before iron therapy. All patients with IDA were treated with elemental iron at a mean dosage of 100 mg/day for 3 months. The HbA1c level was measured using a Variant II Hemoglobin Testing System (BIO-RAD, Hercules, CA, USA) instrument with high-performance liquid chromatography (HPLC). Tests were repeated following iron therapy. The patients with anemia were then divided into three groups according to the total Hb levels: 1) mild anemia (females with Hb ≥11 g/dL and <12 g/dL and males with Hb ≥11 g/dL and <13 g/dL), 2) moderate anemia (Hb ≥8 g/dL and <11 g/dL, for both sexes) and 3) severe anemia (Hb <8 g/dL, for both sexes). The HbA1c results in each group were compared with the HbA1c results in the group without anemia.

Statistical analysis

Statistical analyses were performed using the SPSS version 20.0 software (IBM, Armonk, NY, USA). Categorical variables are expressed in numbers and percentages, whereas continuous variables are expressed in mean and standard deviation (SD) and in median and min–max, where appropriate. The χ2-test was used to compare categorical variables between the groups. Student’s t‑test was used to compare continuous variables between the two groups. The paired samples t‑test was used to compare before-after treatment variables. A p value of <0.05 was considered statistically significant.


Of the total 263 patients, the patient group consisted of 131 patients with IDA and the control group comprised 132 healthy individuals. The mean age of patients with IDA was 39 ± 10 years (range: 19–72 years), and the mean age of the healthy controls was 41 ± 9 years (range: 20–64 years) (Table 1).

Table 1 Laboratory characteristics of patients with iron deficiency anemia (case) and patients without anemia (control)

The number of patients and sexes were similar in both groups. As expected, hematologic parameters between the two groups had significant differences. Hemoglobin, Hct, MCV, and ferritin levels were lower in the patients with anemia (p < 0.05). No difference was seen between the fasting glucose levels in both groups (p = 0.636). In the group with anemia, HbA1c levels were statistically significantly lower (5.4 ± 0.5% and 5.9 ± 0.5%). Of the patients 29 had mild anemia, 31 had moderate anemia, and 2 had severe anemia. Anemia was not observed in 69 patients.

Based on the comparison of the severity of anemia with the HbA1c levels, a decline in HbA1c levels was observed as the hemoglobin levels decreased; however, this difference was not statistically significant (HbA1c levels 5.6%, 5.5%, 5.4%, and 5%, respectively; p > 0.05) (Table 2).

Table 2 HbA1c values according to the severity of anemia (case)

The HbA1c levels of the patients with IDA were higher after iron therapy (from 5.4 ± 0.5 to 5.5 ± 0.3; p = 0.057). The mean Hb, Hct, MCV, MCH, and ferritin values also increased after iron therapy (p < 0.05) (Table 3).

Table 3 Pretreatment and posttreatment variables


Hemoglobin A1c is a glycosylated hemoglobin A1 molecule that shows blood glucose levels over the past 3 months. It is influenced by several factors such as hemolytic anemia, hemoglobinopathy, acute and chronic hemorrhage, blood transfusion (reason for storage conditions) [17], pregnancy, uremia, and blood glucose. In recent years, however, it has become an issue of concern as to how HbA1c levels change in IDA, which is common and affects a significant part of the population [18]. The results in the literature on the relationship between anemia and HbA1c remain controversial. Brooks et al. showed increased HbA1c levels in adults with IDA without diabetes and decreased HbA1c levels after treatment [11]. In a study by Hansen et al. normal HbA1c levels were observed decreased after anemia treatment [12]; however, no change was observed in HbA1c levels of adults without diabetes and no difference was found after iron therapy [1, 19].

Unlike these studies, HbA1c levels were lower in the group with anemia than in the healthy control group in this study. Actually, although HbA1c levels were slightly lower, they were still in the normal reference range, so they are not of great clinical relevance. In a study by Nitin Sinha et al. [16] that included 50 patients, HbA1c was found to be similarly low in the patient group with anemia, and HbA1c levels were found to increase after 2 months of iron therapy. The patients in the present study received oral iron therapy for 3 months. There was a statistically increase in borderline HbA1c levels after treatment. The reason of the non-significant difference in this study may be related with the oral iron therapy (100 mg/day ferrous sulfate) for a limited period of 3 months; however, a statistically significant improvement was observed with Hb, Hct, and ferritin after treatment (Table 3). This finding indicated that higher HbA1c levels can be obtained if patients receive treatment for a longer time of period (i.e., 6 months) for improved clinical and laboratory results.

Several authors have suggested that the inconsistent results between anemia and HbA1c were due to the method used to measure HbA1c. In a study by Goldstein et al. [20], HbA1c measured using HPLC was increased 2h after a standard breakfast, and erythrocytes were incubated in 0.9% saline at 37 °C for 5h. This increase was explained by the presence of insufficient HbA1c. Rai et al. investigated different methods used for measuring HbA1c. They reported that HbA1c levels were not different when they were measured using colorimetric assays, ion exchange chromatography, and affinity chromatography methods. In the present study, HbA1c was studied using HPLC, which is accepted as a safe and valid method.

The mechanisms causing an HbA1c increase or decrease are not clear. According to studies that showed an increase in HbA1c levels, the globin chain was more easily glycosylated due to changes in the hemoglobin structure quaternary in IDA and iron deficiency. It is suggested that the HbA1c concentration increases linearly with the age of each erythrocyte due to this irreversible process [11, 21]. Coban et al. reported that the higher HbA1c levels in IDA could be explained by an increase in the glycolytic fraction due to the decrease in hemoglobin concentration when the serum glucose is constant. Van Heyningen et al. [19], who were among the researchers who found that HbA1c levels did not change with anemia, reported that both mature and immature erythrocytes were minimally affected by the minimal effect of the hemolytic component in IDA, and thus the erythrocyte life span was normal. Hansen et al. demonstrated that there were no significant differences in HbA1c concentrations in patients with iron deficiency and vitamin B12 deficiency and healthy controls. This can be attributed to the fact that the reason for normal HbA1c levels is the absence of the hemolytic component in IDA, and the presence of a minimal hemolytic component in B12 deficiency.

Based on the severity of anemia, the groups with mild anemia, moderate anemia, severe anemia, and groups without anemia had a non-significant decrease in HbA1c levels when the hemoglobin levels were decreased. The reason for not having a statistically significant decrease was probably due to the limited number of patients and that the number of individuals between the groups was different (there were only two patients in the group with severe anemia). Hematologic parameters (Hb, Hct, MCV, and ferritin) at the end of the third month of the treatment statistically increased, and HbA1c levels showed a borderline significant increase. In another study, Juliana et al. [22] reported that HbA1c results could be affected by the severity of anemia and HbA1c could be used in the diagnosis and follow-up of patients with mild anemia and diabetes.

Study limitations

One of the limitations of the study is the inhomogeneous distribution of the subjects in the study groups. Another limitation is that there were only two patients in the severe anemia group. An important other limitation is its relatively short duration, because a 3‑month follow-up is not sufficient for a chronic disease such as IDA, which requires a longer treatment period. In the patients, IDA was still continuing at the end of the third month; however, at the end of the sixth month, the laboratory parameters were unable to be studied.


It is not possible to fully explain the relationship between the presence of IDA, anemia level, and decreasing HbA1c. Most likely, decreased erythrocyte indices, decreased erythrocyte life span, and altered morphology play a role. Although IDA is the most common nutritional deficiency, the results and mechanisms are still unclear. When considering the prevalence of IDA in society and the common use of HbA1c, how anemia affects HbA1c has become an important issue. Unlike other studies, HbA1c levels were assessed in patients with anemia and in a healthy control group before and after treatment in this study. The relationship between anemia severity and HbA1c levels was also assessed. Nonetheless, further large-scale, long-term studies with homogeneous patient groups are required to establish a conclusion.


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Correspondence to Seher Çetinkaya Altuntaş.

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Conflict of interest

S. Çetinkaya Altuntaş, M. Evran, E. Gürkan, M. Sert, and T. Tetiker declare that they have no competing interests.

Ethical standards

The study protocol was approved by the Ethics Committee of Faculty of Medicine Non-invasive Clinical Trials Ethics Committee of Cukurova University (No: 51/Date: 04.03.2016). Written informed consent was obtained from each participant. The study was conducted in accordance with the principles of the Declaration of Helsinki.

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Çetinkaya Altuntaş, S., Evran, M., Gürkan, E. et al. HbA1c level decreases in iron deficiency anemia. Wien Klin Wochenschr 133, 102–106 (2021). https://doi.org/10.1007/s00508-020-01661-6

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  • Hemoglobin A1c
  • Iron deficiency anemia
  • Diabetes mellitus
  • Anemia
  • Iron therapy