Assessing Kidney Function in Combined Heart-Kidney Transplant Candidates: Challenges and Opportunities

Background: Heart transplant candidates often have concomitant kidney disease, necessitating simultaneous heart-kidney transplantation (SHKT). UNOS outlined GFR cutoffs for allocating heart-kidneys in 2023. A heart transplant (HT) candidate with baseline CKD can qualify for SHKT with GFR<=30 or with sustained AKI if GFR<=25. Unfortunately, there is no guidance for appropriate methods of assessing GFR in these patients with heart failure who can be volume expanded and sarcopenic and hence have inaccurate creatinine based GFR (eGFRcr). While cystatin based GFR (eGFRcys) is an alternative, it is known to have high error rates as well. Methods: We present 5 cases of HT candidates who were evaluated for SHKT. Only one of them (#2) had peripheral edema on exam. As part of pre-transplant evaluation, eGFRcr, eGFRcys, eGFRcr-cys (CKD-EPI 2021), 24-hour urinary creatinine clearance (mClcr) and measured GFR using plasma iohexol clearance (mGFR) were obtained. For mGFR, blood samples were drawn at 2, 4, 6 and 24 hours after iohexol injection and GFR was determined using a two-compartment model with the Brochner-Mortenson correction. Results: There was wide discrepancy between eGFRcr and mGFR, with eGFRcr overestimating mGFR for all five patients (Table 1). eGFRcys and eGFRcr-cys were more similar to mGFR. Urine mClcr did not corelate with mGFR. Conclusion: In HT candidates being evaluated for SHKT, it is essential to have an accurate assessment of GFR. eGFRcr alone is fraught with inaccuracies. Our findings support the use of guideline-recommended eGFRcr-cys (CKD-EPI 2021) with comprehensive evaluation using cystatin C and mGFR. Transplant centers should consider collaborating with laboratory scientists to implement measurement protocols for cystatin C and mGFR for assessing dual organ transplant eligibility. - ID Creatinine (mg/dL) eGFRcr (mL/min/1.73m2) Cystatin C (mg/L) eGFRcys (mL/min/1.73m2) eGFRcr-cys (mL/min/1.73m2) mClcr (mL/min/1.73m2) mGFR (mL/min/1.73m2) 1 1.25 54 2.08 29 38 45 42 2 2.98 24 3.55 15 18 UNK 17 3 1.70 34 2.50 21 26 32 21 4 1.26 49 1.71 36 41 26 35 5 2.27 38 1.96 35 36 23 37