Subclinical hypothyroidism in patients in a population with a high prevalence of thyroid pathology

Background
Subclinical hypothyroidism (SCH) is established when serum thyroid-stimulating hormone (TSH) is above the defined upper limit and serum free thyroxine (FT4) is within the reference range. SCH is often not detected clinically, and its impact on kidney function is under active consideration, but not well established, despite the fact that hypothyroidism is associated with a negative effect on renal function. SCH may also be associated with low GFR.

Objectives
To evaluate the impact of thyroid disfunction on renal function in patients with subclinical hypothyroidism.

Material and methods
The study was conducted on the basis of one centre (n = 1,275), and the total sample was represented by patients with established CKD. After considering inclusion and exclusion criteria according to the Billewicz scale, determination of creatinine, TSH, T3 and T4 level, as well as estimation of GFR, was performed. Patients were then divided according to their TSH level. The results were analysed using Microsoft Excel, STATISTICA software and MedCalc.

Results
A direct relationship of TSH with creatinine (ρ = 0.49; p < 0.001) and an inverse relationship with eGFR (ρ = -0.49; p < 0.001) were found. It was determined that TSH has a good prognostic ability for the prediction of kidney failure (AUC = 0.732; p < 0.001), and with a hormone level more than 3.51 μMO/l, sensitivity will be 64.44% and specificity – 83.87%.

Conclusions
The negative impact of TSH level on CKD progression already exists, while TSH only decreases to subclinical levels. Thus, SCH could be a significant risk factor for CKD.