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FOCUS ON
ENDOCRINOLOGIC DISORDERS
Frank Pucino, Section Advisor
Extreme TSH concentrations associated with increased morbidity
Key point: Data from a large population-based study
of patients treated with long-term synthetic thyroxine (T4) therapy
showed that patients with high thyroid-stimulating hormone (TSH)
concentrations, defined as greater than 4.0 mU/L, and those with
suppressed TSH levels, defined as 0.03 mU/L or less, were at
significantly higher risk for cardiovascular disease, cardiac
arrhythmias, and osteoporotic fractures compared with patients with
normal to low TSH levels.
Finer points: A population-based study of 17,684
adult patients living in Tayside, Scotland, who were treated with T4
replacement therapy for a median follow-up of 4.5 years was conducted to
assess the association between TSH concentrations and the risk of
cardiovascular disease, cardiac arrhythmias, and osteoporotic fractures.
The investigators used data from the TEARS (Thyroid Epidemiology Audit
and Research Study) database, which included patient information from
January 1, 1993, to December 31, 2001. TSH concentrations were followed
once patients achieved steady-state levels (i.e., after the third T4
prescription). Patients were categorized into four groups based on mean
serum TSH concentration over the study period: suppressed TSH (0.03 mU/L
or less, n = 1,070), low TSH (0.04 mU/L to 0.4 mU/L, n = 3,731), normal
TSH (0.4 mU/L to 4.0 mU/L, n = 10,908), and high TSH (> 4.0 mU/L, n =
1,975) levels.
After adjusting for covariates—age, gender, history of
cardiovascular disease, arrhythmias, and osteoporotic
fractures—investigators reported that patients with high or
suppressed TSH concentrations had significantly higher morbidity
compared with patients with normal or low TSH levels. Patients with high
TSH concentrations had adjusted hazard ratios (HR) of 1.95 (95% CI
1.73–2.21) for cardiovascular disease, 1.80 (1.33–2.44) for
arrhythmias, and 1.83 (1.41–2.37) for osteoporotic fractures.
Patients with suppressed TSH levels had adjusted HRs of 1.37
(1.17–1.60), 1.60 (1.10–2.33), and 2.02 (1.55–2.62)
respectively.
What you need to know: Most patients with
hypothyroidism, a condition in which the thyroid gland does not make
enough thyroid hormone, require lifelong treatment with thyroid hormone
replacement to get them to a euthyroid, or normal, state of thyroid
gland function. T4 is the most common treatment given to patients with
hypothyroidism; however, clinicians do not agree about how to manage T4
replacement. Some dose T4 until patients achieve normal TSH levels;
others dose T4 until patients are asymptomatic. Some clinicians are
conservative when dosing for patients who are older or who have a
history of coronary artery disease. The current analysis suggests that
clinicians should dose T4 to achieve normal to low TSH levels, because
these levels are not associated with increased morbidity.
What your patients need to know: Educate patients
receiving long-term T4 replacement therapy about the importance of
adhering to medication and undergoing routine blood tests to ensure that
they are within an optimal and safe dosing range.
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