Kidney Function Assessment Using Cystatin C and Serum Creatinine in Heart Transplantation Recipients: Implications for Valganciclovir Dosing

Abstract

BackgroundAmong heart transplantation (HT) recipients, the accuracy of serum creatinine (sCr)-based estimated glomerular filtration rate (eGFR) may be limited by fluctuations in muscle mass. Cystatin C (cysC) is less influenced by muscle mass; however, its levels may increase with obesity and steroid use. Herein, we: i) longitudinally compared changes in eGFRcysC and eGFRsCr among HT recipients; ii) investigated the association of body mass index (BMI), steroid use and muscle mass with discrepancies between eGFRs; and iii) explored the implications of eGFRcysC use on valganciclovir (VGC) dosing.MethodscysC and sCr were measured in 294 blood samples obtained from 80 HT recipients. Intra-individual differences between eGFRs (eGFRdiffcysC-sCr) were calculated. Negative eGFRdiffcysC-sCrvalues correspond to eGFRsCr > eGFRcysC and positive values to eGFRcysC > eGFRsCr. In a patient subset (n=21), pectoralis muscle measures were derived from computed tomography scans.ResultsMarked differences between eGFRcysC and eGFRsCr were observed, particularly early post-HT (1-week post-HT, median eGFRdiffcysC-sCr−28 ml/min/1.73 m2). eGFRcysC demonstrated stability following a transient post-operative decline, while eGFRsCr decreased in the first year post-HT. Lower BMI and higher prednisone dose displayed a modest association with more negative eGFRdiffcysC-sCrvalues. Conversely, pectoralis muscle measures indicative of greater muscle mass and better tissue quality exhibited a stronger association with more positive eGFRdiffcysC-sCrvalues. eGFRcysC use would have resulted in VGC dose adjustment in 46% of samples, predominantly towards lower doses.ConclusionsAmong HT recipients, eGFRcysC and eGFRsCr markedly differ with implications for VGC dosing. The observed discrepancies may reflect changes in body composition and steroid use.