A recent study in the journal BMC Nephrology by a joint Brazilian and US research team investigated a possible link between low free thyroxine and the rate of chronic kidney disease (CKD) progression. However, a large cohort of patients revealed no such association.*

Hypothyroidism and CKD

In patients with chronic kidney disease (CKD), the thyroid gland often produces a low level of thyroid hormone. Called hypothyroidism, this condition is associated with reduced free thyroxin in a human body and makes the course of CKD more complicated. As a result of reduced thyroid hormone, patients with CKD usually have a faster decline in kidney function.

What They Did

• Retrospective data from 1,610 CKD patients between September 2010 and September 2013 was collected.
• Patients’ average estimated glomerular filtration rate (eGFR) had slowly declined. (eGFR is an estimate of how much liquid and waste is passing from the blood through the numerous small filters in the kidneys called glomeruli.)
• Median follow-up of eGFR and CKD progression was 21 months, with 76% of patients tracked for at least 12 months.

They sought answers to the following questions:

• Does low free thyroxin influence rate of eGFR decline?
• Does proteinuria affect progression of kidney dysfunction in patients with low thyroid? (Proteinuria is excess protein in the urine. In healthy humans, urine has little protein, while an excessive amount of protein points to problems with kidney function.)

What They Found

• Examination of patients showed that proteinuria and age were independently associated with eGFR decline.
• However, eGFR decline was not associated with low free thyroxine.
• Furthermore, there was no link between proteinuria and low free thyroxine.
• In patients without proteinuria, there was an improvement in eGFR despite low thyroid levels.

Unclear Treatment Benefit

Patients with proteinuria have a faster rate of eGFR decline though, unexpectedly, there was no association between low free thyroxine and rate of CKD progression. The authors concluded, therefore, that the benefit of hypothyroidism treatment in patients with CKD needs to be evaluated more thoroughly in future studies.

Read the original article in BMC Nephrology.

*de Souza, A.B.C.; Arantes, M.F.; Zatz, R.; et al. (2020) Influence of low free thyroxine on progression of chronic kidney disease. BMC Nephrology, 21(36).