PREVALENCE OF SUBCLINICAL HYPOTHYROIDISM AND ITS ASSOCIATION WITH TYPE 2 DIABETES MELLITUS IN PATIENTS: A CASE-CONTROL STUDY

Abstract

To determine the prevalence of subclinical hypothyroidism (SCH) and its association with type 2 diabetes mellitus (T2DM) in patients.

Study Design: Case-control study.

Place and Duration: The study was carried out from September 2024 to September 2025 at Jinnah Postgraduate Medical Centre/SMC Karachi

Methods: A total of 126 participants, including 63 patients with established T2DM (age >40 years, diabetes duration ≥2 years) and 63 sex and age-matched non-diabetic controls were included. Fasting venous samples were submitted for TSH, free T3, and free T4 level analysis by chemiluminescence immunoassay methods. A TSH concentration higher than 4.5 mIU/mL with normal free T3 and free T4 levels was defined as SCH.

Results: T2DM patients’ prevalence of subclinical hypothyroidism was 38 (60.3%), normal thyroid function was 24 (38.1%), and subclinical hyperthyroidism was 1 (1.6%). Mean serum TSH was significantly higher in diabetic patients (5.1 ± 2.8 µIU/mL) than in controls (2.4 ± 1.2 µIU/mL; p < 0.001), while free T3 (3.1 ± 0.6 pg/mL) and free T4 (1.3 ± 0.35 ng/dL) remained normal. Thyroid dysfunction was not significantly associated with age group (p=0.78), gender (p=0.48), education level (p=0.39), married status (p=0.64), or frequent exercise (p=0.45).

Conclusion: Subclinical hypothyroidism is surprisingly common in T2DM patients and is closely linked to elevated levels of TSH in the face of normal levels of thyroid hormone. The absence of demographic predictors argues for routine screening for thyroid function in all T2DM patients regardless of age, gender, or lifestyle factors.