The truth about thyroids: delays in diagnosis, misdiagnosis, and questions about treatment

In the United Kingdom, doctors are recalibrating how they diagnose and treat thyroid disorders amid growing concerns that underactive thyroids are often missed or misattributed. An estimated one in 20 people in the UK has a thyroid disorder, a butterfly-shaped gland at the base of the neck that regulates hormones such as T3 and T4, which influence heart rate, temperature and mood.

Symptoms of hypothyroidism—weight gain, fatigue, feeling cold, dry skin and hair—can mirror menopause or depression, complicating diagnosis. While hyperthyroidism (too much thyroid hormone) can cause rapid weight loss, sweating and heart palpitations, the condition most often seen is hypothyroidism, particularly among women who are ten times more likely to be affected. Many patients report long waits for a diagnosis, sometimes years, and describe episodes where clinicians attribute their symptoms to mental health or aging instead of checking the thyroid.

Diagnosis relies on blood tests that measure thyroid-stimulating hormone (TSH) and thyroxine (T4). But experts say the practical definition of normal thyroid function is a moving target: reference ranges vary by lab, age and even gender, making some patients feel inappropriately labeled as normal or abnormal. As a result, some doctors initiate treatment with levothyroxine, a synthetic T4, for people who are only borderline cases. Estimates suggest that as many as 80% of those prescribed levothyroxine have subclinical hypothyroidism—tests that fall into a gray area rather than clearly indicating a disease.

The UK today counts about 1.36 million people on levothyroxine, and prescriptions rose by about 9% between 2016 and 2022, according to recent data cited in medical literature. Potential side effects include an increased risk of osteoporosis and atrial fibrillation, risks that become more pronounced with age. The debate over treatment thresholds has grown as clinicians argue about when to start therapy and whether some patients might benefit from lower targets or more conservative management.

Complicating matters is the fact that the reference ranges used to diagnose thyroid disorders are not standardized nationally. Dr. Salman Razvi, a consultant endocrinologist, has described the practice as a minefield: the cutoffs are often determined by statistical norms drawn from healthy volunteers, not by clinical outcomes in older patients or those with comorbidities. This means that what appears normal on a blood test may not reflect an individual patient’s day-to-day function, and some people may endure symptoms despite a test within the so-called normal range.

Recent research backs the need for nuance. A 2022 study in Plos One found that thyroid hormone levels change with age and differ by sex, suggesting that fixed thresholds may not serve everyone equally. Physicians say that while high TSH with low T4 signals an underactive thyroid, having a slightly higher TSH in one's 80s may not be harmful and could reflect normal aging rather than disease—and treating to a lower threshold could expose older patients to unnecessary risk.

There is also mounting concern about overtreatment. Some experts estimate that a substantial share of patients on levothyroxine, the most prescribed thyroid medicine, may not need it at all, particularly those with borderline results. The long-term benefit of treating subclinical hypothyroidism remains uncertain, especially for older adults. A 2017 New England Journal of Medicine study involving older adults with borderline hypothyroidism found that levothyroxine did not improve fatigue or other key symptoms for many participants. Yet, some studies suggest younger patients in their 40s and 50s might experience cardiovascular benefits from treatment.

In pregnancy, the stakes are higher. A 2021 Lancet analysis indicated that subclinical hypothyroidism can increase the risk of miscarriage and adverse pregnancy outcomes, underscoring the importance of thyroid function assessment in certain cases. At present, routine thyroid testing is not universal during pregnancy, which has prompted calls for targeted screening among women with recurrent miscarriage or related risk factors.

DIY thyroid tests sold by retailers have surged in popularity, offering finger-prick samples sent to laboratories for TSH and T4 analysis. While convenient and affordable in some cases, clinicians urge caution: test results can be influenced by recent infections, time of day, or seasonal variation, and many doctors argue the tests do not replace a clinician’s comprehensive assessment. Experts note that frequent, repeated testing may be necessary to draw meaningful conclusions, which undermines some of the claimed simplicity and cost savings of DIY options.

T3 therapy, which adds the other thyroid hormone (triiodothyronine) to T4 treatment, remains controversial. Some patients report sustained symptoms on levothyroxine alone despite normalized blood tests, suggesting that a subset may benefit from combination therapy. However, evidence on long-term safety and effectiveness is still evolving, and access to T3 has been restricted in some health systems after manufacturers raised prices dramatically, limiting availability for routine use.

Researchers emphasize that the path forward should hinge on individualized care rather than a one-size-fits-all approach. Refining diagnostic thresholds for specific age groups, improving recognition of thyroid-related symptoms, and developing clearer guidelines for when to initiate or discontinue therapy could help reduce both underdiagnosis and overtreatment. More large-scale trials are needed to determine optimal management across different life stages and to distinguish symptoms caused by the thyroid from those arising from other health issues.

Overall, the conversation around thyroid health underscores a broader lesson for health systems: balancing accessible testing with careful interpretation is crucial to ensure patients receive appropriate care while minimizing unnecessary treatment. As researchers continue to investigate the subtle interplay between thyroid function, age, sex, and comorbidities, clinicians say the priority remains listening to patients, reviewing their symptoms in context, and using repeat testing when warranted to guide treatment decisions.