Cystatin C is a sensitive marker for detecting a reduced glomerular filtration rate when assessing chronic kidney disease in patients with rheumatoid arthritis and secondary amyloidosis.
OBJECTIVE
Chronic kidney disease is a predictor of end-stage renal disease, and evaluating the glomerular filtration rate (GFR) is necessary to make a definite diagnosis. We assessed the utility of serum cystatin C (cysC) for identifying a reduced GFR in patients who have rheumatoid arthritis (RA) with secondary amyloidosis.


METHODS
Fifty patients with RA and secondary amyloidosis (mean age 60.9+/-11.2 years; 45 women) were evaluated. The revised 24-h creatinine clearance (r24-hC(Cr)), which was determined by multiplying the original value by 0.719, was used as a reference for the GFR. The screening potential of the serum cysC and some estimates of the GFR calculated from the serum cysC (cysC-eGFR: eGFR(Hoek) and eGFR(Rule)) for detecting a reduced GFR (r24-hC(Cr)<60 mL/min/1.73 m(2)) were analysed.


RESULTS
Both cysC-eGFRs were strongly correlated with the r24-hC(Cr) (eGFR(Hoek), r=0.846, p<0.001; eGFR(Rule), r=0.820, p<0.001). The difference between the average eGFR(Rule) (37.1+/-31.2 mL/min/1.73m(2)) and average r24-hC(Cr) (35.3+/-30.9 mL/min/1.73 m(2)) was small, whereas eGFR(Hoek) and sCr-eGFR were higher than eGFR(Rule) and r24-hC(Cr). In receiver operating characteristic (ROC) curve analyses of a reduced GFR, serum cysC gave a greater area under the curve (AUC=0.958) than the sCr-eGFR (0.939-0.942). The specificity and positive predictive value (PPV) reached 100% when serum cysC >1.365 mg/L was used.


CONCLUSIONS
Serum cysC can identify a reduced GFR more accurately than sCr-eGFRs. Serum cysC >1.09 mg/L (i.e. eGFR(Rule)<60 mL/min/1.73 m(2)) could be a marker of a reduced GFR, and serum cysC >1.365 mg/L would strongly suggest a reduced GFR in patients who have RA with secondary amyloidosis.
Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Faculty of Medicine, Niigata University, Chuoku, Niigata City, Japan.
H
H
Sato
T
T
Kuroda
N
N
Tanabe
J
J
Ajiro
Y
Y
Wada
S
S
Murakami
M
M
Sakatsume
M
M
Nakano
F
F
Gejyo
D000368:Aged; D000686:Amyloidosis / Q000097:blood* / Q000175:diagnosis / Q000453:epidemiology; D019540:Area Under Curve; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000175:diagnosis / Q000453:epidemiology; D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein / Q000032:analysis / Q000378:metabolism; D015331:Cohort Studies; D003404:Creatinine / Q000097:blood; D055316:Cystatin C / Q000032:analysis* / Q000097:blood; D018450:Disease Progression; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011336:Probability; D011379:Prognosis; D012372:ROC Curve; D051436:Renal Insufficiency, Chronic / Q000097:blood* / Q000175:diagnosis / Q000453:epidemiology; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index
D015415:Biomarkers; D055316:Cystatin C; D002097:C-Reactive Protein; D003404:Creatinine