Table 2. Observational/RCT studies.
IDA, iron deficiency anemia; HbA1c, hemoglobin A1c; Hb, hemoglobin; LID, latent iron deficiency; RCT, randomized controlled trials; HPLC, high-performance liquid chromatography
| Source | Sample size | Age group | Study type | HbA1c (%) | Hb level | Result |
| Solomon et al. 2019 [10] | 174 | >18 years | Cross-Sectional | IDA: 6.18+/-1.57 Non-IDA: 7.74+/-1.81 (P<0.05) | IDA: 9.97+/-2.04 Non-IDA: 15.17+/-1.21 (P<0.05) | HbA1c is significantly lower in diabetic with IDA compared with non-IDA (P<0.05) |
| Kalairajan et al. 2019 [11] | Case: 120; Control: 120 | 18-60 years | Prospective Interventional | IDA: 4.62+/-0.30 Non-IDA: 5.45+/-0.28 (P<0.001). After correction: HbA1c: 5.82+/-0.32 (P<0.001) | IDA: 6.8+/-1.08 Non-IDA: 13.4+/-0.35 (P<0.001). After correction: 12.7+/-0.44 (P<0.001) | The significant correlation observed between Hb and HbA1c level (coefficient of correlation: 0.26; P<0.01) |
| Urrechaga 2018 [15] | 661 | >18 years | Cross-Sectional | Female >50 years: 7.0+/-1.5 <50 years: 6/3+/-1.3. Male: >50 years: 7.0+/-1.6 <50 years: 6.7+/-1.6 | LID: >120g/L, IDA: male: <130 g/L, female: <120 g/L | A positive correlation between HbA1c and IDA |
| Madhu et al. 2017 [16] | 122 | 20-70 years | Case-Control | Case: 5.5+/- 0.7. Control: 4.9 +/- 0.5 (P<0.001) | Case: 73.9+/-12.2. Control: 134.3+/-13.2 (P<0.001) | Significantly higher HbA1c in IDA P <0.001 and significant improvement in HbA1c level after oral iron supplementation |
| Alsayegh et al. 2017 [12] | 1580 | 18-71 years | Cross-Sectional | >7 anemia (80.7%), non-anemia (80.4%) <7. Anemia (19.3%), non-anemia (19.6%) | Anemia: male: <130 g/L, female: <120 g/L | Higher prevalence of anemia in the diabetic patient (P<0.001). Furthermore, diabetic peripheral neuropathy and diabetic foot were commonly associated with anemia. However, there was no association between HbA1c and Hb (P=0.887) |
| Inada and Koga 2017 [17] | 35 | Non-IDA 59.0+/-7.8. IDA: 59.1+/-2.2 years | Case-Control | IDA: 6.2+/-0.4%. Non-IDA: 5.7+/-0.3 (P=0.003) | Without anemia: 139+/-0.8. With IDA: 11.1+/-0.9 (P<0.0001) | HbA1c level is higher in gastrectomized subjects with IDA than non-IDA (P=0.003) |
| Esfahani et al. 2017 [18] | 90 (45 cases, 45 control) | 18-65 years | RCT | Pre: case 7.59+/-1.16, control: 7.40+/-1.01. Post: case: 6.80+/-0.85, control: 7.14+/-0.95 (P<0.001) | Pre: case: 11.52+/-0.86, control: 11.3+/-0.73. Post: case: 13.71+/-1.37, control: 11.6+/-1.24 (P<0.001) | Significant improvement in the HbA1c level after treatment with iron therapy in anemia patient with IDA and Type II diabetes |
| Silva et al. 2016 [19] | 122 | 18-77 years | Case-Control | Anemia: 5.6+/-0.4 (HPLC method) 5.7+/-0.4 (Immunoturbidimetry Method). No Anemia: 5.3+/-0.4(HPLC Method) 5.3+/-0.3 (Immunoturbidimetry Method) (P<0.001) | Mild: Male: 11-13 mg/dl. Female: 11-12 mg/dl. Moderate: 8-11 mg/dl. Severe: <8 mg/dl | IDA affects HbA1c value, which depends on the severity of anemia. In cases of mild anemia, there is a minimal effect in HbA1c and can be used as a diagnostic tool for diabetes |
| Hong et al. 2015 [20] | 10665 | >19 years | Cross-Sectional | No Anemia: 5.59+/ 0.01. Non-IDA: 5.44+/-0.03. IDA: 5.70+/-0.02 (P<0.001) | No anemia: 14.4+/-0.1. Non-IDA: 12.3+/-0.1. IDA: 11.5+/-0.1 (P<0.001) | No significant difference in the HbA1c level between IDA and non-IDA. However, in euglycemic and prediabetic, HbA1c is significantly higher in IDA compared to non-IDA |
| Christy et al. 2014 [21] | 120 | >18 years | Case-Control | IDA: 6.87+/-1.4, Non-IDA: 5.65+/-0.69 | Low Hb: Male <12 gm%, female <11 gm% | A positive correlation between IDA and increase HbA1c level, especially in controlled diabetes women and individuals with fasting plasma glucose 100-126 mg/dl |
| Shanthi et al. 2013 [22] | Case: 50. Control:50 | 43.52+/-7.79 | Case-Control | In IDA: 7.6+/-0.5%. Non-IDA: 5.5+/-0.8% (P<0.001) | IDA: 10.6+/-1.4. Non-IDA: 13.4+/-0.96% | The author concluded that there is a significant positive correlation between HbA1c and IDA. So, it is important to screen for IDA before starting the treatment for diabetes |
| Ford et al. 2011 [14] | 8296 | >=20 years | Cross-Sectional | Mean HbA1c 5.28% (in Hb<100g/L) & 5.72% (In Hb >170g/L). Adjusted mean HbA1c, in IDA: 5.56%. Non-IDA: 5.46% (P=0.095) | Prevalence of anemia IDA: 2.3+/-0.2% Non-IDA: 3.2+/-0.3%. Normal Hb with IDA: 4.4+/-0.3%. Normal Hb and normal Iron: 90.1+/-0.4% | A significant positive correlation between Hb concentration and HbA1c concentration. Furthermore, caution should be made in diagnosing diabetes in patients with anemia who are close to the diagnostic threshold (6.5% & 5.7%) and need another method or retesting for diagnosis |
| Villar et al. 2011 [13] | 89 | 18-80 years | RCT | Sub-normal: 7.5 +/-1.3. Normal: 7.6 +/-1.4 (P=0.73) | Sub-normal Hb: 110-129. Normal: 130-149 gm/L | HbA1c did not vary significantly with anemia correction in chronic kidney disease (P>0.05) |