Correlation between thyroid function and proteinuria in patients with chronic kidney disease stages 3 and 4

Proteinuria in the nephrotic range is associated with loss of thyroxine-binding protein, levothyroxine, or both, which may lead to subclinical hypothyroidism. The aim of this study was to correlate thyroid function and proteinuria in patients with stages 3 and 4 chronic kidney disease (CKD), in addition to evaluating whether thyroid function differs in these stages of CKD.

Observational, cross-sectional study including 150 patients with stages 3 and 4 CKD. Thyroid stimulating hormone (TSH), free T4 (FT4) and the urine protein-creatinine ratio (PCR) were analyzed. Proteinuria was defined as ≥ 200 mg/g.

Sixty-four patients (42.6%) had stage 3 CKD, and 86 patients (59.4%) had stage 4 CKD. The median age was 68 years (IQR 61-76), the median TSH was 2.9 µIU/mL (IQR 1.89-4.04), the median FT4 was 1.26 ng/dL (IQR 1.10-1.41), and the median PCR was 315.5 mg/g (IQR 108.3-830). Ninety-one patients (60.6%) had proteinuria. In the total sample and in CKD stage 3, there was a statistically significant positive correlation between PCR and TSH, and a negative correlation between PCR and FT4. There were significant differences in the median age (p = 0.004), estimated glomerular filtration rate (p = 0.002), TSH (p = 0.001) and FT4 (p = 0.05) between the PCR < and ≥ 200 mg/g groups.

The results demonstrated a significant correlation between thyroid function and PCR, which corroborates that urinary protein loss can alter thyroid function in CKD stages 3 and 4. Thyroid function did not differ between CKD stages 3 and 4. STUDY DATASET IS AVAILABLE ON CLINICALTRIALS.

NCT04658524.