Normal levels of free thyroxine can elevate AF risk

Level range should be 'reconsidered and redefined', say researchers

The normal range for thyroid hormone levels may need to be revisited, say US researchers who found patients with free thyroxine levels (fT4) at the high end of the reference range are at increased risk of atrial fibrillation (AF).

Researchers from the Intermountain Medical Centre Heart Institute set out to validate a recent observation from the Rotterdam Study that elevated fT4 levels within the normal range are associated with an increased risk of prevalent and incident AF.

Most of the US patients (88%), with an average age of 63.8 years, had tF4 levels within the normal range.

Those within the hospital’s normal range for fT4 (9.65-19.3 pmol/L, 0.75 to 1.50 ng/dL) were allocated into four quartiles according to their ft4 levels.

The six-year follow-up of more than 170,000 patients showed the risk of prevalent AF was 40% higher among patients in the quartile with the highest fT4 levels compared with