High, suppressed TSH levels linked to CV problems, fractures

For patients taking long-term thyroxine replacement, a low thyroid-stimulating hormone level appears to be less likely associated with dysrhythmias, osteoporotic fractures and cardiovascular disease.

However, patients with a high or suppressed TSH had an increased risk for complications.

Researchers studied 17,684 adults (85.9% women) who were patients at the University of Dundee in Tayside, Scotland. All had received prescriptions for T₄ between 1993 and 2001; about 70% had received at least six months of treatment. The main outcome measures were fatal and nonfatal endpoints for CVD, dysrhythmias and fractures.

Suppressed TSH was defined as <0.03 mU/L (6.1% of population), low TSH as 0.04 mU/L to 0.4 mU/L (21.1%), normal TSH as 0.4 mU/L to 4 mU/L (61.7%), and raised TSH as >4 mU/L (11.2%).

Overall, there were 2,144 episodes of CVD, 562 of osteoporotic fractures and 367 of dysrhythmias.

Patients with high TSH had an increased risk for CVD (HR=1.95), dysrhythmias (HR=1.80) and osteoporotic fractures (HR=1.83) during a median follow-up of 4.5 years compared with patients with a TSH in the laboratory reference range. Results were also high for patients with suppressed TSH for CVD (HR=1.37), dysrhythmias (HR=1.6) and fractures (HR=2.02) compared with those with normal TSH.

Alternatively, patients with a low TSH did not have the increased risk for these outcomes: CVD (HR=1.10); dysrhythmia (HR=1.13); and fractures (HR=1.13).

According to the researchers, there is a “long-standing debate” about the management of T₄ replacement because of a lack of data to guide physicians.

“Most guidelines recommend trying to achieve a ‘normal’ TSH,” the researchers wrote. “Although most current guidelines do not generally recommend this, it may be safe for patients on T4 to have a low but nonsuppressed TSH concentration.”

Flynn RW. J Clin Endocrinol Metab. 2009;95:186-193.