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Evaluation of thyroid function monitoring in people treated with lithium: Advice based on real-world data
Helen L Duce1, Christopher J Duff1,2, Syed Zaidi1
1Department of Clinical Biochemistry, University Hospitals of North Midlands NHS Trust, Stoke-on-Trent, UK.
Insights
Monitoring lithium treatment requires regular thyroid function tests. Studies show frequent 3-month testing, not the recommended 6-month interval, and poor adherence to guidelines for lithium patients.
Area of Science:
- Endocrinology
- Pharmacology
- Clinical Medicine
Background:
- Lithium therapy necessitates regular monitoring of thyroid function to prevent adverse effects.
- National Institute for Health and Care Excellence guidelines recommend 6-monthly serum testing for thyroid function in patients on lithium.
- Adherence to these monitoring guidelines is crucial for patient safety and effective lithium management.
Purpose of the Study:
- To assess conformity to recommended 6-monthly thyroid function testing intervals in lithium-treated patients.
- To investigate the impact of monitoring thyroid function outside the recommended intervals.
- To analyze the timing and manifestation of thyroid dysfunction during lithium therapy.
Main Methods:
- Retrospective analysis of serum lithium and thyroid hormone results from January 2009 to December 2020.
- Inclusion of 266 patients initiating lithium therapy with no prior thyroid abnormalities.
- Examination of test intervals, time to abnormal thyroid-stimulating hormone (TSH), and impact of non-adherence to guidelines.
Main Results:
- The most common testing frequency was 3-monthly (17.3% of intervals), indicating testing more frequently than recommended.
- Thyroid dysfunction predominantly manifests within 3 years, with 91.4% of patients showing abnormal TSH by this time.
- Thyroxine replacement was often delayed, initiated a median of 2 years after starting lithium therapy, despite early subclinical hypothyroidism.
Conclusions:
- Current monitoring practices for lithium patients show poor adherence to the recommended 6-monthly thyroid function testing interval.
- Frequent 3-monthly testing suggests concurrent monitoring with serum lithium levels, leading to unnecessary testing.
- Data support the established 6-monthly testing interval and emphasize the need for improved adherence to guidelines.
Introduction:
Blood test monitoring is essential for the management of lithium treatment and National Institute for Health and Care Excellence guidance recommends 6-monthly serum testing of thyroid function. We examined conformity to these guidelines and the impact of monitoring outside these intervals.
Methods:
We extracted serum lithium and thyroid hormone results at one centre between January 2009 and December 2020. We identified 266 patients who started lithium during this period with no history of thyroid abnormality within the previous 2 years and were at risk of developing thyroid abnormalities. We examined the interval between tests, time between onset of lithium testing and first thyroid-stimulating hormone (TSH) outside the laboratory reference range and assessed impact of testing outside recommended 6-monthly intervals.
Results:
The most common testing frequency was 3 months (±1 month), accounting for 17.3% of test intervals. Kaplan-Meier analysis showed that most thyroid dysfunction manifests within 3 years (proportion with abnormal TSH at 3 years = 91.4%, 19.9% of total patients). In the first 3 months after commencing lithium therapy, eight patients developed subclinical hypothyroidism and had clinical follow-up data available. Of these, half spontaneously normalized without clinical intervention. In the remaining patients, thyroxine replacement was only initiated after multiple occasions of subclinical hypothyroidism (median = 2 years after initiating lithium, range: 6 months to 3 years).
Conclusion:
The peak interval at 3 months suggests that thyroid function is frequently checked at the same time as serum lithium, indicating too frequent testing. Our data support the recommended 6-monthly testing interval and highlight poor adherence to it.
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