ESTIMATION OF GLOMERULAR FILTRATION RATE FROM SERUM CYSTATIN C AND CREATININE IN PATIENTS WITH THYROID DYSFUNCTION ODRE\IVANJE JA^INE GLOMERULSKE FILTRACIJE NA OSNOVU SERUMSKE KONCENTRACIJE CISTATINA C I KREATININA KOD BOLESNIKA SA POREME]AJEM FUNKCIJE [T

Summary: 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/1.73m 2 ; 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/ 1.73m 2 ; 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 Kratak sadr`aj: S obzirom na uticaj tireoidne funkcije na nivo cistatina C i kreatinina, postavlja se pitanje mogu}nosti pravilne procene (GFR) brzine glomerularne filtracije kod bolesnika sa tireoidnom disfunk ci jom. Cilj ove studije je evalu acija vrednosti cistatina C i kreati nina uz procenu (GFR) kod bolesnika sa poreme}ajem funk cije {titaste `lezde. U ispitivanje je uklju~eno 32 bolesnika sa novodijagnostikovanom hipertireozom i 27 bolesnika sa novo dijagnostikovanom hipotireozom. Kontrolnu grupu sa~injava 20 zdravih ispitanika koji odgovaraju ispitivanoj grupi prema starosti i polu. Svim ispitanicima je odre|ena koncentracija fT3, fT4, TSH, kreatinina i cistatina C. Pro cenjena je vrednost GFR jedna~inama na osnovu serumske koncentracije kreati nina, kao i jednainom baziranom na vrednosti cistatina C. Zna~ajno su vi{e 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 statisti~ki su zna~ajno ni`e u grupi hipertireoidnih bolesnika u odnosu na kontrolnu grupu (60,6± 10,2 vs. 76,4±8,6; p<0,01), za razliku od zna~ajno vi{ih vrednosti kreatinina u grupi hipo tireoidnih bolesnika u odnosu na kontrolnu grupu (94,5± 13,2 vs. 76,4±8,6; p<0,01). GFR procenjena MDRD i CKD-EPI jedna~inama u grupi hipertireoidnih bolesnika zna~ajno je vi{a u odnosu na GFR u grupi hipotireoidnih bolesnika (101,6±20,7 vs. 64,1±11,6 mL/min/1,73m 2 ; p<0,01). GFR procenjena jedna~inom baziranom na serumskoj koncentraciji cistatina C u grupi hipertireoidnih ispitanika sta tisti~ki je zna ~ajno ni`a u odnosu na iste vrednosti u grupi hipotireoidnih subjekata (59,2± 22,1 vs. 92,1±16,0 mL/min/1,73m 2 ; p<0,01). Iako se smatra da je cistatin C pouzdan parametar u proceni GFR, senzitivniji od serumske koncentracije kreati ni na, njegova List of abbreviations: GFR -Glomerular filtration rate, MDRD -Modification of Diet in Renal Disease, CKD-EPI -Chronic Kidney Disease Epidemiology Collaboration, TSH -thyroid stimulating hormone, fT3 -free triiodothyronine, fT4 -free thyroxine, PETIA -Particle-Enhanced Turbidimetric Immunoassay, CG -control group, HYPER -hyperthyroid subjects, HYPO -hypothyroid subjects, NS -non-significant