Subclinical hypothyroidism and its clinical relevance in routine practice

Abstract

Subclinical hypothyroidism is defined by elevated serum thyroid-stimulating hormone levels with normal circulating free thyroxine and is commonly identified through routine blood tests. Although patients are often asymptomatic, the condition has been associated with a range of systemic effects, including cardiovascular dysfunction, lipid abnormalities, cognitive changes, and subtle metabolic disturbances. These associations have raised concerns about potential long-term consequences, especially in populations with pre-existing risk factors. The diagnosis remains challenging due to inter-individual variation in TSH levels, age-related shifts in reference ranges, and the nonspecific nature of presenting symptoms. Interpretation of thyroid function tests must consider these variables to avoid overdiagnosis or unnecessary treatment. Evidence on whether levothyroxine therapy improves clinical outcomes in subclinical hypothyroidism remains mixed. While some studies suggest benefits in symptom relief, lipid profile improvement, or cardiovascular risk reduction, others show limited or no benefit, particularly in older adults. Treatment is more strongly supported in patients with TSH levels above 10 mIU/l, pregnant women, or those planning conception. In contrast, younger asymptomatic individuals with mild TSH elevations are often monitored without pharmacological intervention. Management strategies must balance potential benefits with the risk of overtreatment, including iatrogenic hyperthyroidism and its associated complications. Individualized care, guided by symptom profile, risk factors, and patient preferences, is increasingly recognized as the most appropriate approach. Clinical guidelines continue to evolve as more data emerge from randomized trials and longitudinal studies. Despite progress, significant gaps remain in understanding the natural history and optimal management of subclinical hypothyroidism. Future research focused on biomarkers of progression, patient-reported outcomes, and age-specific thresholds may help address these uncertainties and improve clinical decision-making.