L-thyroxine Dampens Renal Function Decline in CKD With SCH

Marlene Busko

June 19, 2013

In patients with stage 2 to 4 chronic kidney disease (CKD) and subclinical hypothyroidism (SCH), thyroid hormone replacement therapy (THRT) with L-thyroxine appeared to dampen the rate of decline in renal function, a new study finds.

The work is published in the June issue of Thyroid by Dong Ho Shin, MD, from Hallym University College of Medicine and Kangdong Sacred Heart Hospital, Seoul, Korea, and colleagues, who say that SCH is defined as elevated serum thyroid-stimulating hormone (TSH) and normal free thyroxine (fT4).

The research suggests that "all CKD patients with an elevated TSH should be treated [with THRT] to preserve or improve renal function" and that "THRT may delay reaching end-stage renal disease," Dr. Shin told Medscape Medical News in an email.

Guidelines Unclear About Whether to Treat SCH

About 4% to 10% of adults have subclinical hypothyroidism, and the prevalence is higher in individuals older than 45, especially women, and patients with CKD, according to the authors. Although THRT "is fundamental" in treating primary hypothyroidism, guidelines are less clear about the value of treating subclinical hypothyroidism with THRT, say the researchers.

They studied 113 patients with stable CKD who were treated at their center with L-thyroxine for subclinical hypothyroidism and who had data for at least 24 months before and after THRT, so they could compare the changes in glomerular filtration rate (GFR) before and after L-thyroxine therapy. The patients had a mean age of 63, and 32% were men.

This study design allowed the investigators to assess whether any positive impact of L-thyroxine therapy on GFR was "consistent in different degrees of renal failure," Dr. Shin explained.

Estimated glomerular filtration rate (eGFR) was calculated from the Modification of Diet in Renal Disease (MDRD) study equation, based on the patients' sex, age, and serum creatinine.

The patients were classed as having:

  • Stage 2 CKD (eGFR 60–89 mL/min/1.73 m2), 57 patients.

  • Stage 3–4 CKD (eGFR 15-59 mL/min/1.73 m2), 56 patients.

The patients received L-thyroxine (Synthyroid, Bukwang Pharmacy) at a dose needed to normalize serum TSH levels. The usual starting dose was 25 µg/day and was increased as needed until the patient attained a normal serum TSH level.

L-thyroxine Delayed Decline to Stage 5 CKD in 80%

On average, before the patients received THRT, eGFR declined by 4.31 mL/min/1.73 m2 each year, but after they received THRT, this slowed significantly, to a decline of 1.08 mL/min/1.73 m2 each year.

Linear regression analysis predicted that, based on the slope of the decline in eGFR prior to THRT, 53 of the 113 patients (46.9%) would reach CKD stage 5 — where they would require dialysis or a kidney transplant — within 10 years.

However, using the altered slope of the decline of eGFR after patients received therapy, it was estimated that only 10 patients (8.8%) would reach this outcome in 10 years. Thus, THRT delayed this outcome in 43/53 (81%) of patients.

Although this was a relatively small, retrospective study, "we believe that the current study is meaningful, as it provides evidence that thyroid hormone benefits renal-function preservation in CKD patients with subclinical hypothyroidism," the authors conclude.

The authors have reported no relevant financial relationships.

Thyroid. 2013;23:654-661. Abstract

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