Effects of subclinical hypothyroidism on nephropathy complicating type 2 diabetes: The Fremantle Diabetes Study Phase II

Context It is uncertain whether subclinical hypothyroidism (SCH) contributes to intrinsic renal dysfunction in people with type 2 diabetes mellitus. Objective To investigate whether SCH persisting over 4 years is associated with incident impairment of renal function in people with type 2 diabetes. Design Longitudinal observational study. Setting Urban population of people with type 2 diabetes living in the community and enrolled in a prospective observational study of diabetes. Participants 725 without known thyroid dysfunction at baseline and at follow-up. Main outcome measures Changes in estimated glomerular filtration rate (eGFR) and urine albumin:creatinine ratio (ACR) in participants stratified by thyroid status at baseline and follow-up into those with euthyroidism or transient or persistent subclinical (SCH)/overt hypothyroidism. Results After a mean ± standard deviation 4.3 ± 0.4 years, 683 participants had stable euthyroidism, 18 transient SCH/overt hypothyroidism and 24 persistent SCH/overt hypothyroidism. No significant changes in (Δ) eGFR were observed in any group. Those with persistent SCH/overt hypothyroidism demonstrated a significant increase in ACR which was not seen in those with euthyroidism and transient SCH/overt hypothyroidism (ΔACR 22.0 ± 81.4 vs 0.4 ± 36.7 and -0.3 ± 5.7 mg/mmol respectively, P = 0.027). Similar results were seen when those with baseline ACR > 30 mg/mmol were excluded. Conclusions Persistent SCH/overt hypothyroidism was associated with incident increased albuminuria not observed in euthyroid participants. Assessment of thyroid function in all patients with T2DM may be indicated, as some previous studies provide evidence that thyroxine replacement may ameliorate albuminuria.