Endocrine Abstracts

JOINT303

Summary and Background: Estimation of glomerular filtration rate(eGFR) is commonly based on biomarkers like creatinine(sCr) and cystatin C (sCysC), which are influenced by various factors, including muscle mass and thyroid status(1)(2). This case report presents a unique challenge in accurately assessing renal function in a patient with Chronic Kidney Disease(CKD) who developed severe hyperthyroidism and extreme weight loss. The patient’s eGFR values significantly differed depending on the biomarker used. This disparity raises concerns about the reliability of these biomarkers in such complex clinical scenarios. While thyroid dysfunction is known to affect both sCr and sCysC levels, the aggregate impact of hyperthyroidism on eGFR in CKD patients remains poorly studied. Previous literature has highlighted the paradoxical effects of hyperthyroidism—where eGFR-Cr is often overestimated and eGFR-CysC is underestimated(3)—yet there is limited evidence to guide clinicians on how to reconcile these findings.

Investigations:

Discussion and Conclusion: To our knowledge, the 2015 study by Suzuki et al. is the only clinical study examining eGFR Cr-CysC in thyroid dysfunction (3). This study demonstrated that overestimation of eGFR-Cr and underestimation of eGFR-CysC in the presence of elevated thyroid hormones could be corrected when the condition was treated. Interestingly, the eGFR Cr-CysC derived from the CKD-EPI-Creatinine-Cystatin Equation remained largely unchanged after resolving the hyperthyroid state. This suggests that eGFR Cr-CysC may be independent of thyroid status, offering more accurate method for renal function assessment. In conclusion, healthcare professionals should be aware of the unreliability of Creatinine and Cystatin-C in hyperthyroid patients. The CKD-EPI-Creatinine-Cystatin Equation shows promise but requires further research to guide its use in patients with both CKD and thyroid disease.

References: 1. Baxmann AC, Ahmed MS, Marques NC, et al. Influence of muscle mass and physical activity on serum and urinary creatinine and serum cystatin C. Clin J Am Soc Nephrol. 2008 Mar;3(2):348-54.

2. Xin C, Xie J, Fan H et al. Association Between Serum Cystatin C and Thyroid Diseases: A Systematic Review and Meta-Analysis. Front Endocrinol (Lausanne). 2021 Nov 19;12:766516.

3. Suzuki Y, Matsushita K, Seimiya M, et al., Paradoxical effects of thyroid function on glomerular filtration rate estimated from serum creatinine or standardized cystatin C in patients with Japanese Graves' disease. Clinica Chimica Acta. 2015 Dec 7;451:316-22.