Thyroid dysfunction is common in both type 1 and 2 diabetes and warrants periodic biochemical screening in all people with diabetes (not just type 1) as part of routine management, according to West Australian researchers.

A review of thyroid status in 1617 participants from the Fremantle Diabetes Study Phase II (FDS2) found that 282 (17.4%) had thyroid disease, many of whom (93) had previously undiagnosed or untreated thyroid dysfunction. Of those with overt thryroid disease, almost 9% had not previously been diagnosed prior to participating in the study.

And when followed up after four years, a further 3% of patients who had normal baseline thyroid function were had new onset thyroid disease that was treated and 4% had undiagnosed thyroid dysfunction, including two (7.4%) of the patients with overt thyroid disease.

And while previous studies had suggested that thyroid dysfunction was more common in patients with type 1 diabetes than type 2 diabetes, the Fremantle study found no significant differences in the prevalence or incidence of thyroid dysfunction by diabetes type.

In patients with known thyroid disease at baseline, more females were affected than males (20.4% vs 3.8%).

The study also found that raised baseline TSH was a poor predictor of future hypothyroidism. In people with a raised baseline TSH, persistent elevation was seen in over half (56.5%) of those not commenced on thyroid replacement therapy during follow-up.

The study authors, including Professor Timothy Davies, noted that current guidelines usually recommend screening for thyroid disease in all people with type 1 diabetes. However there is also likely to be a high incidence of thyroid disorders in patients with type 2 diabetes because they are typically older than those with type 1 disease, they said.

“Thyroid dysfunction, whether diagnosed or detected on biochemical screening, is common in diabetes regardless of type. …This latter observation alone makes an argument for periodic biochemical screening in all people with diabetes (not just type 1) as part of routine management,” they wrote in Clinical Endocrinology.

“These data suggest that contemporary guidelines for thyroid function testing in people with diabetes of any type should address the significant proportion of those with potentially treatable disease who remain undiagnosed.”