Context: Earlier we have shown an increased prevalence of previously diagnosed hypothyroidism in common bile duct (CBD) stone patients and a delayed emptying of the biliary tract in hypothyroidism, explained partly by the missing prorelaxing effect of thyroxine on the sphincter of Oddi contractility.

Objective: In this study the prevalence of previously undiagnosed subclinical hypothyroidism in CBD stone patients was compared to non-gallstone controls.

Patients: All patients were clinically euthyreotic and without a history of thyroid function abnormalities. CBD stones were diagnosed at ERCP (Group 1; n = 303) or ruled out by previous medical history, liver function tests and ultrasonography (control Group II; n = 142).

Main outcome measures: Serum free thyroxine (S-FT4) and thyrotropin (S-TSH) were analysed, and S-TSH above the normal range (> 6.0 mU/L) was considered as subclinical and S-TSH 5.0–6.0 mU/L as borderline-subclinical hypothyroidism.

Results: 5.3% and 5.0% (total 10.2%; 31/303) of the CBD stone patients were diagnosed to have subclinical and borderline-subclinical hypothyroidism, compared to 1.4% (P = 0.05) and 1.4% (total 2.8%, 4/142; P = 0.026) in the control group, respectively. In women over 60 years, the prevalence of subclinical hypothyroidism was 11.4% in CBD stone and 1.8% in control patients (P = 0.032), and subclinical plus borderline-subclinical hypothyroidism 23.8% in CBD stone and 1.8% in control patients (P = 0.012).

Discussion: Subclinical hypothyroidism is more common in the CBD stone patients compared to non-gallstone controls, supporting our hypothesis that hypothyroidism might play a role in the forming of CBD stones. At least women over 60 with CBD stones should be screened for borderline or overt subclinical hypothyroidism.