Objective: To evaluate the effect of iron overload on regulation glucose metabolism (diabetes and prediabetes) by using fasting blood glucose level and 2- hour postprandial plasma glucose level.
Methods: This cross-sectional study was carried out at Jamila Sultana Thalassemia center for a period of 6 months. 54 (25 males and 29 females) patients of 12-26 years age, of Thalassemia major on regular blood transfusions and iron chelating therapy were included in the study. Demographic data was taken and standard Body Mass Index was measured for each patient. Fasting plasma glucose levels were checked following an overnight fast, after that each patient was given an oral glucose challenge of 1.75gm/kg body weight with a maximum dose of 75gm. Post-prandial plasma glucose levels were checked two hours after this oral glucose challenge. The data were entered on Statistical Package for the Social Scientists vr. 21 for analysis. Mean and standard deviation were calculated for all quantitative data, frequencies and percentages were calculated for qualitative data.
Results: 13% of the patients had impaired fasting blood glucose, 5.6% patients had impaired 2-hour postprandial levels and 2 patients had their levels were in diabetic range. Patients’ age and Body Mass Index showed a positive correlation with 2- hour postprandial glucose level with highly significant p- value (<0.001).
Conclusion: The findings highlight the importance of regular follow-up of patients with β-thalassemia major patients for early detection and management of associated complications.
Key words: Iron overload, Beta Thalassemia, Impaired glucose level, Glucose regulation, Diabetes, Pre-diabetes.
Beta Thalassemia (BT) is the most common autosomal co-dominant disorder with 5–8% carrier rate in Pakistan. Every year 5000–9000 children are born with beta thalassemia major (TM).¹ It is caused by mutation in beta globin gene resulting in deficiency or absent beta chain. The condition results in severe anemia due to hemolysis and ineffective erythropoiesis, requiring lifelong transfusion. Multiple transfusions result in iron overload and deposition of iron in various tissues. With advancing age, iron deposition is markedly elevated and causes toxic effects in various organs like heart, liver and endocrine glands.
This results in significant morbidity and mortality especially in patients without monitoring of meticulous iron chelation therapy. Iron chelation therapy and hydroxyurea are the mainstay of treatment. Proper iron chelation therapy is mandatory to reduce serum ferritin level and to prevent iron deposition in these vital organs.² Patients with poor compliance to chelation therapy develop complications of iron overload earlier. Regular assessment of iron status is thus essential for effective management of these patients and serum ferritin is the most reliable and widely used indicator of iron overload in various organs.³˒⁴
Endocrine complications are among the most important complications associated with suboptimal chelation therapy. The frequent endocrine complications include hypogonadism, delayed puberty, growth retardation, diabetes mellitus (DM), impaired thyroid, parathyroid and adrenal functions. Early detection and treatment of endocrine complications is of utmost importance to prevent irreversible damage to these organs. DM and glucose intolerance are one of the commonest complications in Beta Thalassemia patients due to iron overload. The prevalence of diabetes and glucose intolerance is 9.4% and 7.1% in Beta Thalassemia major patients and 2% and 24% in Beta Thalassemia Intermedia (TI) patients.⁵˒⁶
Various mechanisms are involved in pathogenesis of diabetes in Beta Thalassemia Major patients. These include hemochromatosis resulting in insulin deficiency, insulin resistance and impaired glucose metabolism in liver due to iron overload, and hepatitis C infection.⁷ Immune mechanisms and inflammatory markers, and iron overload are associated with impaired insulin sensitivity. Risk factors for development of diabetes in these patients include age, serum ferritin level, frequency of transfusions, compliance with iron chelation therapy, family history of diabetes and infection with hepatitis viruses.⁸ A ferritin level of >3000 has been found to be associated with high risk of development of diabetes.⁹ Iron accumulation in the tissues causes free radical injury leading to lipid peroxidation of cell membrane, mitochondrial and lysosomal membrane.¹⁰ It is recommended that iron mediated diabetes can be partially reversed if treated earlier. Early screening and detection of glucose impairment and insulin resistance is recommended in all thalassemic patients from 8–10 years, so that the disease can be halted.¹¹˒¹²
According to American Diabetes Association guidelines, in conditions associated with increased red blood cell turnover, such as Thalassemia, sickle cell disease, pregnancy (second and third trimesters), hemodialysis, recent blood loss or transfusion, or erythropoietin therapy, only plasma blood glucose criteria should be used to diagnose diabetes.
Table 1: Diagnostic Criteria for Diabetics and Pre-Diabetics¹³
| Parameters | Impaired | Diabetes |
|---|---|---|
| Fasting Glucose* | 100–125 mg/dL (5.6–6.9 mmol/L) | >126 mg/dL (7.0 mmol/L) |
| 2 hr Post Prandial** | 140–199 mg/dL (7.8–11.0 mmol/L) | >200 mg/dL (11.1 mmol/L) |
| HbA1c level | 5.7–6.4% (39–47 mmol/mol) | >6.5% (48 mmol/mol) |
*Fasting is defined as no caloric intake for at least 8 hours.
**Post prandial should be performed using a glucose load containing the equivalent of 75 g anhydrous glucose dissolved in water.
The present study was designed to evaluate the effect of iron overload on regulation of glucose metabolism (diabetes and prediabetes) by using fasting blood glucose level and 2 hour postprandial plasma glucose level.
This cross-sectional study was carried out at Jamila Sultana Thalassemia center for a period of 6 months. 54 patients of Beta Thalassemia major coming for regular follow up were included in the study. Sample size calculated from WHO sample size calculator where confidence level = 95%, Anticipated population proportion = 29.4% 2, Absolute precision required = 12%. Patients of Thalassemia major patients of both genders, presenting in routine follow up at Jamila Sultana Thalassemia center, more than 12 years of age and on regular blood transfusions and iron chelating therapy were included in the study and selected by purposive sampling. Acutely ill patients with ongoing severe infections like pneumonia and UTI, patients on steroids or those treated with bone marrow transplantation were excluded from the study. Informed consent was taken from each patient or his/her guardian. Demographic data was taken and weight, height and BMI were measured for each patient. Fasting plasma glucose levels were checked following an overnight fast after which each patient was given an oral glucose challenge of 1.75gm/kg body weight with a maximum dose of 75gm. Post-prandial plasma glucose levels were checked two hours after this oral glucose challenge. Each patient’s Performa was filled by the same doctor. All the available serum ferritin levels for each patient were also noted from the available records. The data were entered on Statistical Package for the Social Scientists (SPSS) version 21 for analysis. Mean and standard deviation were calculated for all quantitative data (age, blood sugar levels). Frequencies and percentages were calculated for qualitative data.
Abnormal Glucose Regulation: It includes a fasting blood glucose level of 100 mg/dl or more and a post-prandial blood glucose level of 140 mg/dl or more. These blood glucose levels were determined through a standard oral glucose tolerance test (OGTT). Pre diabetics show impaired levels
Diabetes Mellitus: It includes fasting blood glucose level of 126mg/dl or more and a post prandial blood glucose level of 200mg/dl or more (table 1).
Thalassemia Major: Patients who were diagnosed to have thalassemia before the age of 2 years, based on hemoglobin electrophoresis (which showed markedly raised levels of hemoglobin F and reduced levels of hemoglobin A1 and required regular blood transfusions since then.
Out of 54 patients, 25 (46.3%) were males and 29 (53.7%) were females. The mean age of the patients was 16.13 ± 3.670 years, ranging from 12–26 years. Table 2 shows the BMI, serum ferritin levels, fasting glucose, and 2-hour postprandial plasma glucose levels. As shown in the table, the mean serum ferritin level was 4912.9 ± 1661.469 ng/L, mean fasting glucose was 87.05 ± 10.458 mg/dL, and mean 2-hour postprandial glucose was 105.01 ± 36.792 mg/dL.
The results of impaired fasting and 2-hour postprandial glucose levels in the study population showed that 13% of patients had impaired fasting blood glucose, 5.6% had impaired 2-hour postprandial levels, and 2 patients had values in the diabetic range. Table 3 shows the correlation of age, BMI, and serum ferritin levels with plasma glucose levels. As shown, age and BMI demonstrated a positive correlation with 2-hour postprandial glucose levels, whereas correlation with serum ferritin was not statistically significant.
Table 2. Evaluation of Different Parameters of Study Population (n = 54)
| Parameter | Range | Mean ± SD |
|---|---|---|
| Age (years) | 12–26 | 16.1 ± 3.670 |
| Weight (kg) | 21–72 | 32.7 ± 8.639 |
| Height (feet) | 3.80–5.70 | 4.70 ± 0.406 |
| BMI (kg/m²) | 12.52–24.91 | 16.04 ± 2.329 |
| Serum Ferritin (ng/L) | 2174–11057 | 4913 ± 1661.469 |
| Fasting Blood Glucose (mg/dL) | 72–124 | 87.1 ± 10.458 |
| 2-hour Blood Glucose (mg/dL) | 58–284 | 105 ± 36.792 |
Table 3. Correlation of Serum Ferritin Level and Other Parameters with Glucose Levels (n = 54)
| Parameter | Fasting Glucose (Pearson correlation) | P value | 2-hour Postprandial Glucose (Pearson correlation) | P value |
|---|---|---|---|---|
| Serum Ferritin Level | 0.092 | 0.509 | 0.045 | 0.745 |
| BMI | 0.398 | 0.003 | 0.493 | 0.000 |
| Age | 0.199 | 0.148 | 0.616 | 0.000 |
Iron overload is the main problem in patients with Beta Thalassemia Major, resulting in various metabolic complications which are usually seen after 10 years of age. Diabetes mellitus is the most common among these, and its etiology is multifactorial (genetic factors, insulin deficiency, insulin resistance, and liver dysfunction secondary to viral hepatitis).¹⁴
In this study, among thalassemic adolescents with a mean ferritin level of 4912.9 ± 1661.469, 13% of patients had impaired fasting blood glucose, 5.6% had impaired 2-hour postprandial glucose, and 2 patients had their levels in the diabetic range. In a study by Najafipour et al. on 56 patients of Thalassemia Major with mean age of 15.62 ± 4.44 years, diabetes mellitus was present in 5 patients (8.9%), impaired fasting glucose in 16 patients (28.6%), and impaired glucose tolerance in 4 patients (7.1%).¹⁵
Various risk factors for diabetes have been reported in these patients, including age, number of blood transfusions, serum ferritin level, compliance with iron-chelating therapy, family history of diabetes, and pubertal status. Other studies have shown similar findings, reporting 10%, 10.4% and 5% cases with diabetes, and 7.1%, 14.6% and 8% cases with impaired glucose tolerance respectively.¹⁶–¹⁸ In our study, its association was found with age and BMI. Najafipour et al. also reported that the risk factors for impaired glucose metabolism were age, number of transfusions, and duration of transfusion therapy.
The high prevalence of diabetes mellitus in patients with thalassemia is not only due to direct impairment of insulin secretion by chronic iron overload. It has also been reported that immune system activation against pancreatic β-cells due to iron deposition and oxidative damage acts as an environmental trigger for autoimmunity, contributing to selective β-cell destruction. This highlights that good iron chelation is essential for preventing diabetes in these patients.
Chronic Hepatitis C also shows a strong association with abnormal glucose tolerance. Khalifa et al. reported 100% positivity for Hepatitis C in patients with abnormal GTT.¹⁷ Another cross-sectional study comparing HCV-positive and HCV-negative Beta Thalassemia Major patients reported a higher prevalence of diabetes among HCV-positive adults (15.2% vs. 1.9%, p = 0.02). However, no significant difference was observed in younger (8–15 years) patients. It is probable that hemosiderosis enhances the impact of HCV infection on glucose metabolism.¹⁸
A study from Egypt on glucose homeostasis and oxidative stress in children and adolescents with Beta Thalassemia Major reported that patients with irregular chelation therapy had significantly higher fasting glucose, 2-hour post-load plasma glucose, serum ferritin, ALT, fasting insulin, and HOMA-IR compared with healthy controls. Oxidative stress markers (OSI and plasma MDA) were significantly elevated, while serum TAC (Total Antioxidant Capacity) was significantly decreased (P < 0.001 for each). Moreover, HOMA-IR was positively correlated with age, serum ferritin, ALT, and MDA, and negatively correlated with TAC.¹⁹ Similar studies can be carried out in our local population as well.
Intensive combined chelation therapy (oral plus subcutaneous) over a period of 24–36 months has been shown to improve glucose metabolism disorders.²⁰ A study conducted by Platis reported an overall prevalence of impaired fasting glucose (IFG) = 16.7% and diabetes mellitus = 12.5%. They also observed that dry liver iron concentration (LIC) correlated significantly with serum ferritin levels (r = 0.512; p = 0.011). Impaired fasting glucose was significantly higher in Beta Thalassemia Major patients with very high LIC (>30 mg Fe/g dry liver) compared to those with lower LIC (p = 0.044).²¹
A cross-sectional study of 48 Beta Thalassemia patients receiving hyper-transfusions reported a 12.5% prevalence of impaired glucose tolerance in those with suboptimal chelation therapy. The clinical features of thalassemia patients who developed impaired glucose tolerance included wasting, stunting, higher ferritin levels, splenectomy, and lower insulin levels due to pancreatic β-cell damage.²²
The study emphasizes the importance of regular follow-up of patients of β-thalassemia major for early detection and management of associated complications. Because not all of the patients with thalassemia major could be correctly diagnosed by fasting glucose alone, we preferred to use the oral glucose tolerance test rather than fasting blood glucose for the diagnosis of abnormal glucose tolerance in thalassemic patients. It is thus recommended that A 2-hour oral glucose tolerance testing, preferably combined with insulin secretion determination, should be performed at 10-12 years of age and annually thereafter. Moreover, if fasting serum glucose is >110 mg/dl at any stage, OGTT is indicated.
Conflict of interest: None to declare
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