Abstract
AIM: The thyrotropin controversy in subclinical thyroid disorders (STDs) is among the most common endocrine disorders globally. In India, approximately 42 million people suffer from thyroid disorders, with subclinical hypothyroidism (SCH) affecting about 9.4% of the population. SCH is more prevalent in females (11.4%) compared to males (6.2%).
DISCUSSION: The diagnosis and treatment of SCH and subclinical hyperthyroidism (SHT) are controversial. SCH is often diagnosed based on biochemical markers, as patients may be asymptomatic or exhibit vague symptoms. Thyrotropin (TSH) levels may be elevated or decreased, while triiodothyronine (T3) and thyroxine (T4) remain within the normal reference range or near the lower or upper limits. STDs refers to an abnormal TSH with normal thyroxine (FT4) and free triiodothyronine (FT3) levels. It includes STDs and individuals at high risk for disease progression or adverse outcomes, with unclear prognosis. Progression of SCH to overt hypothyroidism depends on initial serum TSH levels, thyroid peroxidase antibodies (TPO), family history of thyroid disorders, previous radiation, and smoking. Controversies surround SCH and its association with cardiovascular diseases (CVD), pregnancy outcomes, neuropsychiatric issues, metabolic syndrome, dyslipidemia, and diabetes. Assay interference is a problem in interpreting thyroid function tests (TFTs), occurring in 1% of cases. The health package investigation systems often overlooks the impact of drug intake and assay interference. Various methods for measuring TFTs, such as radioimmunoassay, immunometric assay, and ELISA, differ in sensitivity, specificity, and standardization, leading to methodological variability. Common causes of assay interference include human antimurine antibodies (HAMA), thyroid hormone autoantibodies (THAAbs), rheumatoid factor, antistreptavidin, and antiruthenium antibodies. When diagnosing SCH, it is crucial to rule out other causes of elevated TSH, such as autoantibodies, goiter, and rare conditions such as thyroid hormone resistance (THR), diagnosed by serum glycoprotein alpha subunit (α-GSU) and family history. Biotin, a common supplement, can affect TFT assays, leading to spurious results. It can cause falsely high T4 and T3 levels and low TSH, leading to misdiagnosis of SCH.
CONCLUSION AND RECOMMENDATIONS: The timing of TFTs, whether fasting, postprandial, or random, remains a debated issue. Assay interference and biotin intake should be considered when analyzing TFTs. The role of iodine and iodine supplementation during pregnancy and its impact on STDs are not yet fully conceptualized. Large randomized clinical and epidemiological studies are needed to establish a consensus on the diagnostic threshold for TSH. These studies should include diverse populations and medical conditions to improve our understanding of the disease and patient outcomes. In practice, avoid rushing to treat elevated TSH levels between 4 and 10 mIU/L or low TSH between 0.5 and 0.1 mIU/L without confirming the diagnosis with additional tests (T3, T4, FT4, FT3, and TPO). TSH alone should not be the sole decision-maker; consider other TFTs and sequential testing from the same laboratory and time to make more informed decisions. While TSH levels can be affected by time and prandial state, FT3 and FT4 levels remain stable, suggesting all three TFTs may aid in accurate diagnosis and treatment decisions.