Endocrine Abstracts

Background: Serum cystatin C is a novel marker for kidney function that has been claimed to be superior to serum creatinine. Cystatin C concentrations increased in the hyperthyroid patients and decreased in the hypothyroid patients. The cystatin C test detects kidney disease at earlier stages, before symptoms appear and creatinine levels rise. Another advantage is that, unlike creatinine, blood levels of cystatin C are less influenced by age, gender, race, or lean muscle mass, which makes it a better indicator of kidney function. This study was performed to evaluate changes in cystatin C and creatinine during the treatment of subclinical hypothyroidism (SH).

Methods: Cystatin C, creatinine, CRP and lipids were determined at the time of diagnosis of SH (TSH>4.2 mIU/ml with normal level of fT3 and fT4), and when TSH returned into the normal range after treatment with levothyroxine in 35 SH women ages 35.3±9.5 years.

Results: TSH was 9.4±4.3 mU/l (reference 0.3–4.2) at diagnosis and decreased to 2.9±1.2 mU/l following treatment with levothyroxine. Cystatin C increased from 0.68±0.19 mg/l (reference 0.5–0.96) in the hypothyroid state to 0.89±0.16 mg/l when TSH normalized (P<0.01). Creatinine decreased from 98±11 μmol/l (reference 45–115) in the hypothyroid state to 67±14 umol/l when TSH normalized (P<0.05). CRP levels also decreased when TSH normalized (5.2±1.1 vs 2.5±0.9 mg/l). Mean total and LDL-cholesterol levels decreased too, but not significantly.

Conclusion: Subclinical hypothyroidism has a substantial impact on cystatin C levels. In contrast to creatinine concentrations, Cystatin C levels are lower in the hypothyroid state as compared with the euthyroid state. Therefore, thyroid function has to be considered when cystatin C is used as a marker of kidney function at many diseases like diabetes, hypertension, and cardiovascular diseases.