Subclinical Hypothyroidism - Think twice before testing or treating

What is it they say about the three certainties in life? Death, taxes and life in the NHS never gets any quieter? We’re all no doubt gearing up for another busy winter, so any evidence or guidelines that can help rationalise and (safely) reduce our workload, however small, can be very welcome. Our patients will also be thankful - reducing unnecessary testing and treatment burdens remains an important part of our job.

I was ploughing through path results this week, and alongside mountains of lipid results, another test I saw lot of was thyroid results, many of which fell into the ‘subclinical hypothyroid’ category. It’s an area which can generate a lot of re-testing and potentially inappropriate treatment, so this is a ‘good news’ review - an area where we can safely reduce further tests for our patients and reduce workload in our practices! 

The data and guidelines underpinning this are a few years old now, but remain highly relevant still. First a brief re-cap on subclinical hypothyroidism (SCH) which is defined as a raised TSH with normal thyroxine (usually free T4) levels. It is incredibly common in normal populations, affecting up to 20%, and of those with TSH levels between 4-10 mIU/L, 60% will normalise within 5 years. Many people with SCH will report non-specific symptoms that could be attributable to hypothyroidism (e.g. fatigue, skin changes etc.) but given those are such common symptoms anyway, the relationship between the TSH and symptoms is often unclear and may well be an ‘association not causation’. 

A large meta-analysis, subsequently reviewed in the BMJ (BMJ 2019;365:l2006) led to a practical clinical guideline from the BMJ, which highlighted that the evidence consistently demonstrated no benefit from treating SCH with regard to quality of life or thyroid related symptoms and that thyroid hormones may have little or no effect on CV events or mortality. They concluded with a strong recommendation against treatment with thyroid hormones for most adults with SCH. Importantly, this excludes those with very high TSH levels >20, those with very severe symptoms, young adults <30 and women who are pregnant/planning pregnancy. 

So for the majority with SCH treatment isn’t needed, but for some with symptoms consistent with hypothyroidism NICE do advocate a 6 month trial of thyroxine if SCH persists (i.e. at least 2 tests at least 3 months apart and remember to check if they are taking biotin supplements which can affect results), particularly if TSH levels >10, but importantly if the TSH normalises and symptoms persist we should stop the thyroxine.

So that should help rationalise treatment but what about re-testing? Again I suspect many of us are retesting more than we need, particularly in older adults. About 30% of older adults are having TFTs done every year at a cost of tens of millions of pounds. Evidence from the Birmingham Elderly Thyroid Study showed the risk of people aged >65 with SCH developing overt hypothyroidism is extremely low; this led to a NIHR recommendation that ‘it is safe for GPs not to routinely retest older adults (aged >65) unless they have risk factors or develop clinical symptoms of overt thyroid dysfunction’. 

Less testing and treatment that lowers burdens for patients and reduces our workload that is evidence based - it’s a thumbs up from me! Click here for our 1 page KISS that summaries the assessment and management of subclinical hypothyroidism.