Serum Cystatin C versus Creatinine Based Assessment of Renal Function in Heart Transplant Patients

Purpose Serum creatinine (sCr) is routinely used in the assessment of renal function among heart transplant (HT) pts. However, changes in muscle mass and nutritional status early post-HT may affect the accuracy of sCr estimated glomerular filtration rate (eGFRsCr). While Cystatin C (CysC) is independent from the above mentioned confounders, an increase in CysC with steroid use has been reported. The ratio sCr/CysC has been validated as a marker of muscle mass. Herein, we aimed to: i) longitudinally compare post-HT changes in CysC eGFR (eGFRCysC) and eGFRsCr; and ii) investigate the relation of muscle mass, nutritional status and steroid use with the difference between eGFRCysC and eGFRsCr. Methods Pts transplanted between 6/2016 and 4/2019 had serial, concurrent measurements of CysC and sCr pre- and post-HT. Albumin (a marker of nutritional status) and prednisone dose at the time of sample collection were recorded. Adjusted linear mixed models were used to: i) regress post-HT changes in eGFRCysC, eGFRsCr and sCr/CysC ratio; ii) study associations of albumin and prednisone dose with the difference between eGFRsCr and eGFRCysC (ΔeGFRsCr-CysC = [eGFRsCr - eGFRCysC]/eGFRsCr). Results 313 samples were collected in 84 pts (age 54±12, 20% female). While eGFRsCr declined long-term, eGFRCysC showed an opposite trend with a gradual improvement (Figure). The temporal decline in eGFRsCr mirrored the progressive rise in sCr/CysC ratio, suggesting a contribution of an increase in muscle mass to this decline. Albumin was inversely related to ΔeGFRsCr-CysC (β= -0.51, p Conclusion eGFRCysC and eGFRsCr markedly differ early post-HT. Changes in muscle mass and nutritional status as well as steroid use may account for the observed discrepancies. Future studies are warranted to address these inconsistencies as accurate estimation of renal function carries important clinical implications (e.g. medication dosing).