Background: Cystatin C is a low molecular weight (12.8 kDa) protein synthesized by all nucleated cells whose physiological role is that of a cysteine protease inhibitor. Compared to serum creatinine, Cystatin C has a lower interindividual variability and is not correlated to lean tissue mass, gender, and age. Cystatin C has been proposed as a good marker of GFR, particularly in patients with moderate to severe renal impairment. Hence, this study was undertaken to evaluate the serum Cystatin C levels in subclinical hypothyroidism. 

Materials and methods: Patients with newly diagnosed subclinical hypothyroidism were included in the study. Subclinical hypothyroidism was defined as free thyroxine (fT4) within normal range and Thyroid stimulating hormone(TSH) above normal range. Total of 22 patients with subclinical hypothyroidism were included in the study. Serum Cystatin C levels were decreased in cases when compared to control, which is highly significant (<0.001).

Conclusion: Our study has shown the impact of subclinical hypothyroidism of Cystatin C levels, which was significant. So, it is advisable to know the thyroid status of on individual when Cystatin C is measured to know the GFR.