Estimation of Glomerular Filtration Rate From Serum Cystatin C and Creatinine in Patients with Thyroid Dysfunction

Estimation of Glomerular Filtration Rate From Serum Cystatin C and Creatinine in Patients with Thyroid Dysfunction Given that thyroid function influences serum cystatin C and creatinine levels, the question arises as to whether it is possible to accurately estimate glomerular filtration rate (GFR) in patients with thyroid dysfunction. The objective of the study was to determine serum cystatin C and creatinine levels and estimate GFR in patients with thyroid dysfunction. The study included 32 cases with newly diagnosed hyperthyroidism and 27 cases with newly diagnosed hypothyroidism, as well as 20 healthy controls matched for sex and age with the cases. Serum concentrations of thyroid stimulating hormone (TSH), free triiodothyronine (fT3) and free thyroxine (fT4), creatinine and cystatin C were measured in all study subjects. GFR was estimated using the Modification of Diet in Renal Disease (MDRD), the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and cystatin C-based equations. Serum cystatin C levels were significantly higher in hyperthyroid subjects compared to controls (1.32±0.31 vs. 0.89±0.15; p<0.01). Serum creatinine levels were significantly lower in hyperthyroid subjects compared to controls (60.6±10.2 vs. 76.4±8.6; p<0.01), and significantly higher in hypothyroid subjects compared to controls (94.5±13.2 vs. 76.4±8.6; p<0.01). GFR estimated with the MDRD equations was significantly higher in hyperthyroid subjects compared to hypothyroid subjects (101.6±20.7 vs. 64.1±11.6 mL/min/1.73m2; p<0.01). GFR estimated with the equation based on serum cystatin C was significantly lower in hyperthyroid subjects compared to hypothyroid subjects (59.2±22.1 vs. 92.1±16.0 mL/min/1.73m2; p<0.01). Although serum cystatin C is regarded a reliable marker of GFR and more sensitive than serum creatinine, it has limitations in patients with thyroid dysfunction, due to significant changes in its serum concentrations regardless of renal function. In patients with thyroid dysfunction GFR should therefore be estimated using the equations based on serum creatinine. Određivanje Jačine Glomerulske Filtracije na Osnovu Serumske Koncentracije Cistatina C i Kreatinina Kod Bolesnika sa Poremećajem Funkcije Štitaste Žlezde S obzirom na uticaj tireoidne funkcije na nivo cistatina C i kreatinina, postavlja se pitanje mogućnosti pravilne procene (GFR) brzine glomerularne filtracije kod bolesnika sa tireoidnom disfunkcijom. Cilj ove studije je evaluacija vrednosti cistatina C i kreatinina uz procenu (GFR) kod bolesnika sa poremećajem funkcije štitaste žlezde. U ispitivanje je uključeno 32 bolesnika sa novodijagnostikovanom hipertireozom i 27 bolesnika sa novodijagnostikovanom hipotireozom. Kontrolnu grupu sačinjava 20 zdravih ispitanika koji odgovaraju ispitivanoj grupi prema starosti i polu. Svim ispitanicima je određena koncentracija fT3, fT4, TSH, kreatinina i cistatina C. Procenjena je vrednost GFR jednačinama na osnovu serumske koncentracije kreatinina, kao i jednačinom baziranom na vrednosti cistatina C. Značajno su više vrednosti cistatina C u grupi hipertireoidnih bolesnika u odnosu na kontrolnu grupu (1,32±0,31 vs. 0,89±0,15; p<0,01). Vrednosti kreatinina statistički su značajno niže u grupi hipertireoidnih bolesnika u odnosu na kontrolnu grupu (60,6± 10,2 vs. 76,4±8,6; p<0,01), za razliku od značajno viših vrednosti kreatinina u grupi hipotireoidnih bolesnika u odnosu na kontrolnu grupu (94,5± 13,2 vs. 76,4±8,6; p<0,01). GFR procenjena MDRD i CKD-EPI jednačinama u grupi hipertireoidnih bolesnika značajno je viša u odnosu na GFR u grupi hipotireoidnih bolesnika (101,6±20,7 vs. 64,1±11,6 mL/min/1,73m2; p<0,01). GFR procenjena jednačinom baziranom na serumskoj koncentraciji cistatina C u grupi hipertireoidnih ispitanika statistički je značajno niža u odnosu na iste vrednosti u grupi hipotireoidnih subjekata (59,2± 22,1 vs. 92,1±16,0 mL/min/1,73m2; p<0,01). Iako se smatra da je cistatin C pouzdan parametar u proceni GFR, senzitivniji od serumske koncentracije kreatinina, njegova upotreba je ograničena kod bolesnika sa tireoidnom disfunkcijom usled značajnih promena njegove serumske koncentracije nezavisno od bubrežne funkcije, odnosno, kod bolesnika sa tireoidnom disfunkcijom za procenu GFR treba koristiti jednačinu baziranu na serumskoj koncentraciji kreatinina.