European Journal of Cardiovascular Medicine

Anaemia, characterised by a reduction in haemoglobin concentration or red blood cell mass, remains a prominent global public health issue, affecting around one-quarter of all people worldwide (1). The endocrine system plays a significant but often under-recognised role in haematological homeostasis. Among endocrine disorders, hypothyroidism—defined by insufficient production of thyroid hormones—has been increasingly implicated in the pathogenesis of various types of anaemia (2).

Hypothyroidism results from a spectrum of aetiologies including autoimmune destruction of the thyroid gland (such as Hashimoto’s thyroiditis), iodine deficiency, thyroidectomy, and therapeutic irradiation, among others (2). Thyroid hormones, particularly thyroxine (T4) and triiodothyronine (T3), exert important regulatory effects on erythropoiesis: they stimulate erythroid progenitor cell proliferation, enhance erythropoietin production, and influence iron metabolism, all of which are essential for maintaining adequate red cell mass (3,4).

Several observational studies and meta-analyses have documented a significantly higher prevalence of anaemia in patients with overt and subclinical hypothyroidism compared with euthyroid individuals. A large individual participant data meta-analysis found that participants with overt hypothyroidism had 1.84 (95 % CI: 1.35–2.50) times higher odds of anaemia compared to euthyroid participants (3). Other studies have reported the prevalence of anaemia in hypothyroid patients ranging between approximately 40 % and 70 % (4,5).

The mechanisms linking hypothyroidism and anaemia are multifactorial and include:

• Reduced thyroid hormone–mediated erythropoietin production and impaired erythroid progenitor stimulation (2,5).
• Altered iron metabolism (including decreased iron absorption, altered ferritin and transferrin levels) and associated iron-deficiency states (6).
• Bone marrow suppression, decreased red-cell survival, and concomitant nutritional deficiencies (vitamin B12, folate) or chronic disease (7,8).

Given this background, the clinical and haematological correlation between anaemia and hypothyroidism warrants systematic investigation. Despite the evidence of association, the specific patterns of haematological abnormalities (such as types of anaemia—normocytic, microcytic, macrocytic) and their correlation with thyroid hormone parameters (TSH, free T4, free T3) remain variably reported across different populations (9). For example, one study found normocytic anaemia to be the most common type in primary hypothyroid patients (38.6 %), followed by microcytic (19.3 %) and macrocytic (9.3 %) (4).

Therefore, the present study titled “Assessment of Anaemia in Patients with Hypothyroidism: Clinical and Haematological Correlation” aims to evaluate the prevalence and types of anaemia in patients with hypothyroidism, and to correlate haematological indices with thyroid hormone parameters and clinical profiles. This will help clarify the burden of anaemia in this specific endocrine disorder, the spectrum of haematological changes observed, and potential implications for diagnosis and management in clinical practice.

This was a hospital-based cross-sectional observational study conducted in the Department of Medicine in collaboration with the Department of Biochemistry, at Dr. Patnam Mahender Reddy Institute of Medical Sciences, Chevella a tertiary care teaching hospital. The study was carried out over a period of 12 months after obtaining institutional ethical committee approval.

The study included clinically and biochemically diagnosed patients with hypothyroidism attending the outpatient and inpatient departments. Diagnosis of hypothyroidism was based on serum thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels.

A total of 100 patients were enrolled in the study using a convenient sampling method. The sample size was calculated considering a prevalence of anaemia of approximately 40–60% among hypothyroid patients from previous studies [2,4], at a 95% confidence interval and 10% allowable error.

Inclusion Criteria

1. Adult patients aged 18–60 years of either sex.
2. Patients newly diagnosed or known cases of primary hypothyroidism (overt or subclinical) confirmed by biochemical tests.
3. Patients who provided written informed consent to participate.

Exclusion Criteria

1. Patients with known hematological disorders (e.g., thalassemia, aplastic anaemia, leukemia).
2. Patients with chronic liver disease, renal failure, malignancy, or infections affecting blood indices.
3. Patients on iron, vitamin B12, or folic acid supplementation in the preceding three months.
4. Pregnant women or those with postpartum thyroiditis.

Ethical Considerations

Approval for the study protocol was obtained from the Institutional Ethics Committee (IEC) prior to initiation. Written informed consent was obtained from each participant after explaining the purpose and procedures of the study in their local language.

Method

Detailed clinical history was recorded, including demographic data, duration of disease, medication history, dietary pattern, and symptoms suggestive of anaemia (fatigue, pallor, dyspnea). A thorough clinical examination was performed with emphasis on pallor, thyroid enlargement, and signs of hypothyroidism.

Under aseptic precautions, 5 mL of venous blood was collected from each participant after overnight fasting:

• 2 mL in EDTA vial for complete blood count (CBC) analysis using an automated hematology analyzer (e.g., Sysmex KX-21 or equivalent) to determine haemoglobin (Hb), red blood cell (RBC) count, hematocrit (PCV), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), and mean corpuscular haemoglobin concentration (MCHC).
• 3 mL in plain tube was allowed to clot, centrifuged, and serum separated for biochemical assays:
• Serum TSH, FT4, and FT3 measured by electrochemiluminescence immunoassay (ECLIA) using
• Serum iron, total iron-binding capacity (TIBC), and ferritin estimated using standard colorimetric or chemiluminescent methods.
• Vitamin B12 and folate levels determined in selected cases to classify macrocytic anaemia.

Classification of Hypothyroidism

• Overt hypothyroidism: Elevated TSH (>10 mIU/L) with low FT4 levels.
• Subclinical hypothyroidism: Elevated TSH (4.5–10 mIU/L) with normal FT4 levels.

Classification of Anaemia

Anaemia was defined according to WHO criteria:

• Males: Hb <13 g/dL
• Females: Hb <12 g/dL

Anaemia was further classified morphologically based on

MCV values:

Statistical Analysis

Data were entered into Microsoft Excel and subsequently analyzed using Statistical Package for the Social Sciences (SPSS) version 25.0. Quantitative variables such as haemoglobin concentration, red blood cell indices, and thyroid hormone levels were expressed as mean ± standard deviation (SD), while qualitative variables like gender distribution and types of anaemia were presented as percentages and proportions. The Independent t-test and Analysis of Variance (ANOVA) were applied to compare mean values between different study groups. Associations between categorical variables were assessed using the Chi-square test. To determine the degree of linear relationship between thyroid function parameters (TSH, FT4, FT3) and haematological indices (Hb, MCV, MCH, MCHC), Pearson’s correlation coefficient (r) was calculated. A p-value less than 0.05 was considered statistically significant for all analyses

Table 1. Demographic Profile of Study Participants (n=100)

Out of the 100 hypothyroid patients studied, the majority were in the 41–50 years age group (32%), followed by 31–40 years (28%), indicating that hypothyroidism predominantly affects middle-aged adults. Females constituted 78% of the total cases, reaffirming the well-documented female predominance of thyroid disorders due to hormonal and autoimmune susceptibility. The majority of participants were from urban areas (62%), reflecting better healthcare access and diagnosis rates in urban populations. Regarding disease duration, 42% had hypothyroidism for 1–3 years, suggesting a chronic disease pattern. In terms of BMI, most patients were overweight (42%) or obese (26%), consistent with the metabolic slowing associated with hypothyroidism. The most common clinical symptoms observed were fatigue (85%), weight gain (72%), dry skin (64%), and cold intolerance (61%), along with pallor in 58%, indicating concurrent anaemia in many cases

Table 2:  Distribution of Study Subjects According to Type of Hypothyroidism (n = 100)

Among the study participants, 62% had overt hypothyroidism, while 38% had subclinical hypothyroidism. This finding suggests that a significant proportion of patients present with clinically and biochemically established thyroid hormone deficiency, although a sizable subgroup exhibits subclinical disease detected incidentally through biochemical testing. These proportions align with the global trend showing overt hypothyroidism as more prevalent among clinically symptomatic patients.

Table 3:  Distribution of Anaemia Among Hypothyroid Patients

Anaemia was identified in 58% of the hypothyroid patients, indicating a high prevalence of anaemia in this population. This highlights that thyroid dysfunction substantially impacts erythropoiesis, possibly through decreased erythropoietin levels and impaired iron metabolism. The remaining 42% of patients maintained normal haemoglobin levels, suggesting variable hematological involvement depending on disease duration, severity, and nutritional status

Table 4:  Morphological Types of Anaemia in Hypothyroidism (n = 58)

Among the 58 anaemic patients, the normocytic normochromic type was most prevalent (44.8%), followed by microcytic hypochromic anaemia (34.5%) and macrocytic anaemia (20.7%). The predominance of normocytic anaemia suggests a hypometabolic suppression of bone marrow activity, whereas microcytic anaemia may reflect concurrent iron deficiency due to menstrual loss or malabsorption. Macrocytic cases could be attributed to vitamin B12 or folate deficiency, common in autoimmune thyroid disorders.

Table 5 :  Comparison of Hematological Parameters Between Anaemic and Non-Anaemic Hypothyroid Patients

The mean haemoglobin level in anaemic patients was 9.84 ± 1.12 g/dL, significantly lower than 13.21 ± 0.94 g/dL in non-anaemic subjects (p < 0.001). Similarly, RBC count, PCV, MCV, MCH, and MCHC were all markedly reduced in anaemic patients, with all differences being statistically significant (p < 0.05). These findings confirm that hypothyroidism adversely affects multiple hematological indices, reflecting both reduced erythropoietin activity and impaired nutrient utilization necessary for erythropoiesis.

Table 6 :  Comparison of Thyroid Profile Between Anaemic and Non-Anaemic Patients

The mean TSH level was significantly higher in anaemic patients (18.94 ± 7.12 µIU/mL) compared to non-anaemic ones (11.82 ± 5.93 µIU/mL, p < 0.001), while FT4 and FT3 were significantly lower in anaemic individuals (p < 0.001 for both). This pattern indicates that the severity of hypothyroidism correlates directly with anaemia severity, emphasizing the metabolic influence of thyroid hormones on red-cell production and survival

Table 7 :  Correlation Between Thyroid Hormone Parameters and Haematological Indices (n = 100)

A negative correlation was found between TSH and haematological parameters such as haemoglobin (r = –0.412) and RBC count (r = –0.368), while positive correlations were observed between FT4 and FT3 with these indices (r = +0.438 and +0.406, respectively). All correlations were statistically significant (p < 0.05). This indicates that as thyroid function deteriorates, erythropoietic activity declines, whereas improved thyroid hormone levels enhance red-cell parameters. Hence, the study establishes a strong clinical and biochemical link between thyroid dysfunction and anaemia

The present study was conducted to evaluate the prevalence, type, and severity of anaemia in hypothyroid patients and to determine its correlation with thyroid hormone levels. Hypothyroidism has been increasingly recognized as an important metabolic disorder influencing erythropoiesis through decreased erythropoietin production, iron utilization, and bone marrow activity [11,10]. The discussion below integrates our findings table-wise with observations from previous Indian and international research.

In the present study, the majority of patients were in the 41–50 years age group (32%) with a strong female predominance (78%), consistent with the hormonal and autoimmune predisposition in women. Similar demographic profiles were observed by Kale et al. (2017) and Goyal et al. (2019), where over 70% of hypothyroid patients were female [2,8]. Fatigue (85%), weight gain (72%), and pallor (58%) were the most common symptoms, comparable to reports by Dorgalaleh et al. (2013) and Chaker et al. (2019) [9,3]. The predominance of overweight and obese patients in our study (68%) also aligns with metabolic slowing observed in hypothyroidism [12].

Overt hypothyroidism was seen in 62% and subclinical in 38% of cases, indicating that clinically evident thyroid hormone deficiency predominates among symptomatic patients. Kale et al. (2017) reported overt hypothyroidism in 60% of their cohort [2], while Kumar et al. (2023) and Ali et al. (2024) found similar proportions of 63% and 66%, respectively (4,13). The consistency of these findings highlights that anaemia is more prevalent in overt cases, possibly due to more pronounced metabolic impairment.

In the present study, 58% of hypothyroid patients were anaemic, which falls within the reported global range (40–70%). Chaker et al. (2019) demonstrated a 1.84-fold higher risk of anaemia in overt hypothyroidism compared to euthyroid individuals [3]. Similarly, Goyal et al. (2019) found a prevalence of 61.7%, and Das et al. (2012) reported 54% in their Indian cohorts [8,7]. Kawa et al. (2010) also confirmed that thyroid dysfunction significantly alters haematopoiesis [10]. This reinforces that hypothyroid states, particularly overt forms, are strongly linked to anaemia.

Normocytic normochromic anaemia (44.8%) was most common in our study, followed by microcytic (34.5%) and macrocytic (20.7%) types. Patel et al. (2017) reported a similar distribution with 46% normocytic, 35% microcytic, and 19% macrocytic patterns [2]. Kumar et al. (2023) and Das et al. (2012) also found normocytic anaemia to be predominant [4,7]. The higher frequency of normocytic type suggests a hypometabolic suppression of bone marrow, while microcytosis indicates iron deficiency, and macrocytosis may relate to autoimmune gastritis-associated B12 or folate deficiency in Hashimoto’s thyroiditis [14].

Anaemic hypothyroid patients showed significantly lower mean haemoglobin (9.84 ± 1.12 g/dL) compared to non-anaemic ones (13.21 ± 0.94 g/dL; p < 0.001). All RBC indices (MCV, MCH, MCHC) were significantly reduced, reflecting both quantitative and qualitative impairment of erythropoiesis. These findings correspond with those of Dorgalaleh et al. (2013) and Hajjar and Brown (2017), who observed decreased RBC indices and packed cell volume among hypothyroid individuals [9,5). Goyal et al. (2019) and Kibirige & Mwebaze (2013) also reported lower haematological parameters in hypothyroid subjects [8,6). Hence, thyroid hormone deficiency appears to affect multiple erythroid parameters simultaneously.

Patients with anaemia had significantly higher TSH (18.94 ± 7.12 µIU/mL) and lower FT4 (0.68 ± 0.21 ng/dL) and FT3 (2.31 ± 0.51 pg/mL) compared to non-anaemic subjects, showing a strong negative correlation between thyroid hormone levels and anaemia severity. Similar trends were observed by Chaker et al. (2019) and Kumar et al. (2023), where lower FT4 was associated with reduced haemoglobin [3,4]. Goyal et al. (2019) also reported a significant difference in TSH and FT4 levels between anaemic and non-anaemic groups [8]. This supports the hypothesis that the severity of thyroid dysfunction directly influences erythropoietic suppression.

In our study, TSH correlated negatively with haemoglobin (r = –0.412) and RBC count (r = –0.368), while FT4 and FT3 correlated positively with these indices (r = +0.438 and +0.406, respectively). These results mirror the findings of Dorgalaleh et al. (2013) and the large-scale pooled analysis by Chaker et al. (2019), which confirmed inverse relationships between TSH and haematological parameters [9,3]. Ali et al. (2024) also reported similar correlations, indicating that rising TSH and declining thyroid hormones are accompanied by declining erythroid parameters [13].

The present study demonstrates a strong clinical and hematological correlation between hypothyroidism and anaemia. More than half of the hypothyroid patients were anaemic, with normocytic normochromic anaemia being the most common type, indicating a hypometabolic suppression of erythropoiesis rather than isolated nutritional deficiency. The severity of anaemia increased with higher TSH levels and lower FT3/FT4 values, confirming that thyroid hormone deficiency directly affects red-cell production and maturation. These findings emphasize the importance of routine haematological evaluation in hypothyroid patients for early detection and management of anaemia, which may improve overall clinical outcomes and quality of life.

Acknowledgement: None

Conflict of Interest: None

1. Voskaridou E, Christoulas D, Terpos E. Endocrine dysfunction in patients with hematologic disorders: An underrecognized problem. J Clin Endocrinol Metab. 2022;107(2):e643–e658.
2. Kale P, Bhalerao A, Pandav C, Gadgil A, More S. Study of anemia in primary hypothyroidism. Thyroid Res Pract. 2017;14(1):6–10.
3. Chaker L, Cappola AR, Mooijaart SP, Peeters RP. Associations of thyroid function with anemia: A pooled analysis of individual participant data. J Clin Endocrinol Metab. 2019;104(11):5850–5860.
4. Kumar P, Kannan R, Arumugam P, Saravanan A. Prevalence and pattern of anemia in patients with hypothyroidism: A prospective observational study. 2023;15(8):e43592.
5. Hajjar V, Brown RS. Thyroid hormone and erythropoiesis: A review of the connection and clinical implications. Thyroid Res Pract. 2017;14(1):10–15.
6. Kibirige D, Mwebaze R. Thyroid hormone abnormalities among patients with diabetes mellitus: A review. Afr Health Sci. 2013;13(3):661–668.
7. Das C, Sahana PK, Sengupta N, Ghosh A, Roy M, Chowdhury S. Thyroid disorders in patients with chronic anemia: A cross-sectional study. Indian J Endocrinol Metab. 2012;16(Suppl 2):S361–S365.
8. Goyal A, Arya V, Pathania M, Mehta A. Hematological profile and anemia patterns in hypothyroidism: A study from tertiary care hospital. Int J Adv Med. 2023;10(4):307–313.
9. Dorgalaleh A, Mahmoodi M, Varmaghani B, Zare M, Kiani Node F, Alizadeh S, et al. Effect of thyroid dysfunctions on blood cell count and red blood cell indices. Iran J Ped Hematol Oncol. 2013;3(2):73–77.
10. Kawa MP, Grymuła K, Paczkowska E, Baśkiewicz-Masiuk M, Dąbkowska E, Koziołek M, et al. Clinical relevance of thyroid dysfunction-induced anemia. Endocr J. 2010;57(10):873–879.
11. Wopereis DM, Du Puy RS, van Heemst D, et al. Relation between thyroid function and anemia: a pooled analysis of individual participant data. J Clin Endocrinol Metab. 2018;103(10):3658–3667.
12. Floriani C, Gencer B, Collet TH, Rodondi N. Subclinical thyroid dysfunction and cardiovascular diseases: 2018 update. Eur Heart J. 2018;39(7):503–507.
13. Ali SS, Dawood H, Al-Fadhli S, et al. Frequency and types of anemia in primary hypothyroidism. 2024;16(1):e52340.
14. Das KC, Mukherjee M, et al. Prevalence and characteristics of macrocytosis in autoimmune thyroid disease. J Clin Pathol. 2016;69(2):173–178.