Thyroid dysfunction prevalence and relation to glycemic control in patients with type 2 diabetes mellitus

It is usually difficult to clinically identify thyroid abnormalities in diabetics as features of thyroid dysfunction may simulate diabetes symptoms or complications. So, assessing thyroid dysfunction prevalence in patients with type 2 diabetes mellitus (DM) would help better control of DM and its complications. Several studies reported this prevalence, however, some included small sample size or lacked a control group. We aimed to determine thyroid dysfunction prevalence in diabetic patients as well as its relation to glycemic control.

A cross-sectional study included 200 patients having type 2 DM and 200 apparently healthy controls. Each participant was tested for fasting and 2-h post-prandial blood glucose, glycated haemoglobin (HbA1C), thyroid function tests: thyroid-stimulating hormone (TSH), free tri-iodothyronine (FT3), free thyroxine (FT4), serum total cholesterol and triglycerides and thyroid antibodies; anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-Tg) for hypothyroidism only.

There was a significant increase in serum TSH and T3 levels in diabetics when compared with the controls, (P < 0.001, P = 0.001), respectively. Thyroid dysfunction was significantly more prevalent in patients with HbA1c ≥ 8%, (P = 0.0001), and in those having longer diabetes duration, (P < 0.001).

There was a higher prevalence of thyroid dysfunction among patients with type 2 DM. This dysfunction increased with the rise of HbA1c. This could suggest that poor glycemic control may have a role in the development of thyroid dysfunction in type 2 DM patients. Subclinical hypothyroidism was the most prevalent type of thyroid dysfunction in diabetic patients.