Assessment of Renal Function Test and Estimated Glomerular Filtration Rate in Subclinical Hypothyroidism

Introduction:The relationship between renal dysfunction and endocrine functions leading to a hypometabolic state is known.However, there is a lack of data regarding early treatment for subclinical hypothyroidism (SCH).When serum creatinine is elevated in SCH, it demands the need for investigation to assess if the elevated serum creatinine is due to true renal impairment and reduced glomerular filtration rate (GFR).For this, the estimated glomerular filtration rate (eGFR) helps in understanding the pathogenesis of renal involvement. Aims and objectives:The aim of the current study is to assess renal parameters, such as serum creatinine, urea, and uric acid levels in hypothyroid and SCH cases, and compare them with euthyroid patients. Materials and methods:A cross-sectional descriptive study was conducted from August 2019 to January 2020 at a tertiary care center in Bengaluru.A total of 90 hypothyroid female cases (including clinical hypothyroid and subclinical) were enrolled, along with age-matched 100 healthy controls.The Erba EM 360, a fully automated analyzer, was used to estimate serum creatinine, urea, and uric acid.Free triiodothyronine (fT3), free thyroxine (fT4), and thyroid-stimulating hormone (TSH) were analyzed using the Maglumi 800 chemiluminescent immunoassay (CLIA).The modification of diet in renal disease (MDRD) study equation and the chronic kidney disease-epidemiology collaboration (CKD-EPI) equation were utilized for the eGFR calculation.Results were presented as mean ± standard deviation (SD).The unpaired Student's t-test was applied to assess the association between cases and controls.Analysis of variance (ANOVA) was used to compare SCH and overt hypothyroid cases with controls.A p-value of <0.05 was considered statistically significant.Pearson's correlation coefficient was applied to evaluate the correlation between study groups.Result: Both MDRD eGFR and CKD-EPI were decreased in cases compared to controls, with a p-value of <0.01.There were three groups: SCHgroup II (n = 50), clinical hypothyroidism (CH)-group III (n = 40), and controls-group I. Statistically significant differences were observed with eGFR calculated by MDRD and CKD-EPI between SCH, CH, and control groups (p < 0.01).TSH showed a moderate negative correlation with eGFR calculated by MDRD and CKD-EPI, with correlation coefficients of -0.43 (p < 0.01) and -0.47 (p < 0.001), respectively.Conclusion: Kidney function, compromised in thyroid dysfunction, can be early assessed with eGFR.Early diagnosis of kidney damage helps determine the at-risk population and enables timely management and prevention of associated future complications.