Equations with Both Serum Cystatin C and Creatinine Inaccurately Estimate Glomerular Filtration Rate

Sickle cell disease, as debilitating as it is, is associated with the progressive complication of renal damage — beginning with hyerfiltration in childhood to glomerular filtration rate (GFR) decline and chronic renal failure in approximately 12 % of HbSS sickle cell adults.

While albuminuria is a marker of glomerular damage, it doesn’t predict GFR. Marianne E. Yee, MD, MSc, Aflac Cancer and Blood Disorders Center, Children’s Healthcare of Atlanta, Emory University, Atlanta, GA, and her team will present at the 57^th American Society of Hematology Annual Meeting 9ASH 2015) in Orlando, FL, results detailing how serum creatinine and cystatin C can be used to estimate GFR.

Although prior studies using equations incorporating CysC and SCr in young children with SCD had been conducted to compare estimated GFR to measured GFR, they weren’t examined for precision or accuracy of GFR formulas.

Yee and team; however, involved adults and children 10 years and below with HbSS and albuminuria who were already on hydroxyurea therapy for at least six months. To determine the effects on albuminuria and renal hemodynamics, Yee enrolled this patient cohort on a trial of losartan therapy.

They used urinary clearance of intravenous iohexol at baseline to measure GFR — serum creatinine and CysC were measured by standard clinical laboratory techniques. And, compared with previous studies, the researchers made sure to assess accuracy.

The team found that in 15 patients there were 33 iohexol GFR measurements and eight had macroalbuminuria. Also CysC inversely correlated with mGFR and was higher in those experiences stage 2 CKD.

According to the results, the team noted that in adults with HbSS, the equation, which incorporated serum CysC alone without age, sex, race, or SCr best estimated GFR. “Cystatin C correlates with CFR in SCD, and is elevated more frequently in stage 2 CKD, thus it remains an important marker of renal impairment in this population. As direct CFR measurement is not practical in the general clinical setting, further studies are needed to develop eCFR equations with improved accuracy for the SCD population,” concluded the authors.