CHALLENGES AND OPPORTUNITIES IN ASSESSING KIDNEY FUNCTION IN SIMULTANEOUS HEART-KIDNEY TRANSPLANT CANDIDATES

Introduction:

Simultaneous heart-kidney transplantation (SHKT) is a preferred destination therapy for advanced heart and kidney disease, accounting for >1% of all kidney transplants (KT) in the US as compared to 0.2% in 2003. The patient selection was subjective until June 2023 when UNOS published medical eligibility criteria for SHKT candidates based on measured or estimated GFR (mGFR or eGFR). According to these, a heart transplant (HT) candidate with CKD (GFR<60) is eligible for SHKT if the candidate has begun regular dialysis or GFR/CrCl <= 30 ml/min. A HT candidate without CKD will be eligible for SHKT if on dialysis for 6 weeks or GFR/CrCl <= 25 ml/min. Unfortunately, there is wide variation between creatinine-based eGFR (eGFRcr), measured CrCl (mCrCl), and mGFR due to non-GFR determinants of Scr, especially with heart failure due to volume overload, sarcopenia, cardiac cachexia, medication use, and due to measurement errors in timed urine collections. 

Methods:

As part of pre-transplant evaluation for SHKT, eGFRcr and eGFRcr-cys (CKD-EPI 2021) and eGFRcys (CKD-EPI 2012), 24-hour mCrCl, and mGFR using plasma iohexol clearance were obtained. All indexed to BSA (mL/min/1.73m2). Bias (systematic error) was assessed as the mean difference between mGFR and eGFR. Positive bias indicates underestimation of mGFR and negative bias overestimation of mGFR.

Cases:

1. 44y/F with grade III diastolic CHF and CKD G3A1 (eGFRcr 44-54). Evaluated for SHKT due to eGFRcys 29. mGFR was 42 and therefore received isolated HT. Now 9 months post-HT, stable eGFRcr 53-68.

 2. 52y/M with niCMP and CKD G3A3 (eGFR 28-54) from insulin-dependent DM (IDDM) and hypertension (HTN) was evaluated for SKHT. mGFR, performed due to wide fluctuation in eGFRcr, was 17. Underwent SHKT but unfortunately passed away 211 days post-op due to cardiogenic shock and sepsis.

 3. 62y/F with niCMP had CKD G3A1 attributed to cardiorenal syndrome. eGFRcr and mCrCl were >30 but eGFRcys was 21. mGFR was 21, qualifying her for dual listing (awaiting transplant).

 4. 61y/F with niCMP, LVAD implant and CKD G3A1 (eGFRcr 36-44) in the setting of HTN. Referred for SHKT because mCrCl was 26. mGFR was 35, and she was listed for isolated HT.

 5. 33y/M with niCMP had CKD G3A3 from IDDM and HTN. Referred for SHKT for mCrCl 23 despite eGFRcr 38. mGFR was 37, therefore listed for isolated HT.

 6. 54y/M with niCMP and NSVT status post ICD, nonobstructive CAD, IDDM, Afib and CKD G3A1 (eGFRcr 32-40). Referred for SHKT because of low eGFR and discrepant mCrCl. mGFR was 38, therefore listed for isolated HT.

Results:

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Conclusions:

We report wide discrepancy between eGFRcr, eGFRcys, mCrCl and mGFR, with eGFRcr overestimating mGFR (mean overestimation 7.5). eGFRcr-cys was more like mGFR with lowest bias (mean overestimation of mGFR by 1.3).

Only 50% of SHKT recipients were on dialysis and >20% SHKT recipients had GFR >45 at the time of transplant, whereas 87% of isolated KTR are dialysis dependent. Multiorgan recipients also benefit from higher quality organs but have lower patient and graft survival as compared to KTR. Therefore, it is essential that recipients of MOT be carefully selected to optimize equity and utility in transplantation.

The latest UNOS medical eligibility criteria for SHKT, while defining GFR cutoffs, fail to acknowledge the errors in eGFRcr as described through our cases. Centers should be cognizant of errors in eGFRcr and use guideline-recommended eGFRcr-cys to make decisions about eligibility for SHKT.

I have no potential conflict of interest to disclose.

I did not use generative AI and AI-assisted technologies in the writing process.