Electrolyte Disorders in Kidney Transplantation

Calcium phosphate deposition, tertiary hyperparathyroidism, and the long-term effect on kidney allografts

BACKGROUND

Tertiary hyperparathyroidism adversely affects kidney allografts, with calcium phosphate deposition hypothesized to be an underlying cause. We analyzed allograft biopsies to investigate risk factors for calcium phosphate deposition and understand its impact on allograft function.

METHODS

We reviewed patients who underwent kidney transplantation from 2017 to 2019. Tertiary hyperparathyroidism was defined as an elevated parathyroid hormone and hypercalcemia beyond 3 months' posttransplant or being prescribed cinacalcet. Allograft failure was defined as needing dialysis posttransplantation or retransplantation beyond 3 months' posttransplant. Three- and 12-month allograft biopsies were reviewed for calcium phosphate deposition. The χ2, t-test, and multivariate regression were used for statistical analysis.

RESULTS

Of 159 patients who underwent kidney transplantation, 59 (37.1%) were diagnosed with tertiary hyperparathyroidism. Longer preoperative dialysis vintage (odds ratio, 1.47; confidence interval, 1.22-1.80 P < .001) and preoperative cinacalcet usage (odds ratio, 18.4; confidence interval, 7.24-53.0 P < .001) were associated with tertiary hyperparathyroidism. In total, 36 of 59 (61%) patients with tertiary hyperparathyroidism had calcium phosphate deposition on 3- or 12-month kidney allograft biopsy compared with 23 of 100 (23%) patients without tertiary hyperparathyroidism (P < .001). Tertiary hyperparathyroidism (odds ratio, 6.01; confidence interval, 2.91-13.0 P < .001) was associated with calcium phosphate deposition. Calcium phosphate deposition and tertiary hyperparathyroidism were not associated with worse glomerular filtration rate at 3 years' posttransplantation. Of those with data available at 3 years' posttransplantation, 21 of 49 (42.9%) patients remained on cinacalcet. There were 3 of 159 (2%) patients who had allograft failure, 2 of whom had both tertiary hyperparathyroidism and calcium phosphate deposition.

CONCLUSION

Preoperative variables associated with tertiary hyperparathyroidism included longer dialysis vintage and cinacalcet use. Tertiary hyperparathyroidism was the main risk factor for calcium phosphate deposition posttransplantation. In our population, calcium phosphate deposition and tertiary hyperparathyroidism were not significantly associated with lower glomerular filtration rate.

Electrolyte and Acid-Base Abnormalities After Kidney Transplantation

Kidney transplantation is the optimal therapeutic approach for individuals with end-stage kidney disease. The Scientific Registry of Transplant Recipients has reported a continuous rise in the total number of kidney transplants performed in the United States, with 25,500 new kidney recipients in 2022 alone. Despite an improved glomerular filtration rate, the post-transplant period introduces a unique set of electrolyte abnormalities that differ from those encountered in chronic kidney disease. A variety of factors contribute to the high prevalence of hypomagnesemia, hyperkalemia, metabolic acidosis, hypercalcemia, and hypophosphatemia seen after kidney transplantation. These include the degree of allograft function, immunosuppressive medications and their diverse mechanisms of action, and metabolic changes after transplant. This article aims to provide a comprehensive review of the key aspects surrounding the most commonly encountered electrolyte and acid-base abnormalities in the post-transplant setting.

Factors Associated With Persistent Post-transplant Hyperparathyroidism After Index Renal Transplantation

INTRODUCTION

Secondary hyperparathyroidism (SHP) is common in end-stage renal disease and may progress to persistent post-transplant hyperparathyroidism (PTHP) following renal transplantation (RT). We sought to describe the frequency and determine factors associated with the incidence of PTHP for patients undergoing RT at a single institution that restricts RT for patients with uncontrolled SHP with a parathyroid hormone (PTH) of >800pg/mL at time of initial transplant evaluation.

METHODS

We conducted a single-institution retrospective study of adults undergoing index RT from 2012 to 2020 who had a calcium and PTH level within 12 mo prior to RT and at least 6 mo following RT. PTHP was defined as calcium of >10 mg/dL with an elevated PTH > 88pg/mL at six or more months following RT. Univariate analysis and multivariable logistic regression were performed for factors associated with developing PTHP.

RESULTS

We identified 1110 patients with RT, 65 were excluded for prior RT, 549 did not have a pre-RT and post-RT calcium, and PTH laboratories for inclusion, yielding 496 for analysis. Following RT, 39 patients (7.9%) developed PTHP, compared to those who did not develop PTHP; these patients had significantly higher pre-RT PTH, pre-RT calcium, and frequency of calcimimetic therapy. In multivariable logistic regression factors significantly associated with PTHP were pre-RT calcium of more than 10 mg/dL with an odds ratio (OR) of 3.57 (95% confidence interval [CI] 1.52-8.39, P = 0.003) and pre-RT calcimimetic therapy with an OR 1.30 (95% CI 1.06-2.85, P = 0.041). Compared with patients who had a pre-RT PTH of less than 200 pg/mL, a PTH of 200-399 pg/mL increased risk of PTHP with an OR of 4.52 (95% CI 1.95-21.5, P = 0.048) and a PTH of > 400 pg/mL increased risk of PTHP with an OR of 7.17 (95% CI 1.47-34.9, P = 0.015). In this cohort, 11 patients (28.2%) with PTHP underwent parathyroidectomy (PTx) at a mean of 1.4 y post-RT (standard deviation 0.87).

CONCLUSIONS

For patients required to have a PTH < 800pg/mL for initial transplant candidacy, the subsequent incidence of PTHP is relatively low at 7.9%. Risk factors for PTHP include higher pre-RT calcium and PTH levels and pre-RT calcimimetic therapy. PTx remains underused in the treatment of PTHP. Further study is warranted to determine the optimal PTH cutoff for transplant candidacy and recommendation for PTx in patients requiring calcimimetic therapy for SHP.

Non-Traditional Non-Immunological Risk Factors for Kidney Allograft Loss-Opinion

Rates of late allograft loss have improved slowly in the last decades. Well described traditional risk factors that influence allograft survival include cardiovascular events, rejection, infections and post-transplant neoplasia. Here, we critically evaluate the influence of several non-immunological, non-traditional risk factors and describe their impact on allograft survival and cardiovascular health of kidney transplant recipients. We assessed the following risk factors: arterial stiffness, persistent arteriovenous access, mineral bone disease, immunosuppressive drugs residual levels variability, hypomagnesemia, glomerular pathological alterations not included in Banff criteria, persistent inflammation and metabolic acidosis.

The prognostic value of pre-operative coronary evaluation in kidney transplanted patients

Aims

Non-invasive coronary assessment using single-photon emission computerized tomography (SPECT) testing for potential cardiac ischemia is an essential part of the evaluation of kidney transplant candidates. We aimed to examine the prognostic value of preoperative SPECT test results in kidney transplanted patients.

Methods and results

We retrospectively analyzed the pre-surgical nuclear SPECT test results in a registry of kidney transplanted patients. Follow-up at 1 month and 1 year recorded major adverse cardiac events (MACE) including non-fatal myocardial infarction, all-cause mortality and hospitalization due to cardiovascular disease following the renal transplantation. Of 577 patients available for analysis, 408 (70.9%) patients underwent nuclear SPECT test pre-transplant and 83 (20.3%) had abnormal results with either evidence of ischemia or infarct. A significantly higher incidence of post-operative MACE at 1 month was evident among patients with abnormal SPECT test compared to patients with no evidence of ischemia (10.8 vs. 4.3% respectively; P = 0.019). Differences were mostly derived from significantly increased rates of myocardial infarction events (8.4 vs. 1.8%; P = 0.002). Yet, MACE rate was not statistically different at 1 year (20.5 vs. 13.1%; P = 0.88). Importantly, the prognostic impact of an abnormal SPECT was significantly attenuated for all outcomes following multivariable adjusting for conventional cardiovascular risk factors and coronary revascularization.

Conclusion

Pre-surgical cardiac risk assessment of kidney transplant candidates with nuclear SPECT test was found to be predictive of post-operative MACE, yet apparently, its prognostic value was significantly attenuated when adjusted for cardiac risk factors.

Sodium-glucose cotransporter-2 inhibitors (SGLT2i) in kidney transplant recipients: what is the evidence?

Several recent randomized controlled trials (RCTs) have demonstrated the wide clinical application of sodium-glucose cotransporter-2 inhibitors (SGLT2i) in improving kidney and cardiovascular outcomes in patients with native kidney disease. In April 2021, Dapagliflozin became the first SGLT2 inhibitor to be approved by the Food and Drug Administration (FDA) for the treatment of chronic kidney disease (CKD) regardless of diabetic status. However, while these agents have drawn much acclaim for their cardiovascular and nephroprotective effects among patients with native kidney disease, little is known about the safety and efficacy of SGLT2i in the kidney transplant setting. Many of the mechanisms by which SGLT2i exert their benefit stand to prove equally as efficacious or more so among kidney transplant recipients as they have in patients with CKD. However, safety concerns have excluded transplant recipients from all large RCTs, and clinicians and patients alike are left to wonder if the benefits of these amazing drugs outweigh the risks. In this review, we will discuss the known mechanisms SGLT2i exploit to provide their beneficial effects, the potential benefits, and risks of these agents in the context of kidney transplantation, and finally, we will discuss current findings of the published literature for SGLT2i use in kidney transplant recipients and propose potential directions for future research.

Clinical factors associated with severe hypophosphataemia after kidney transplant

BACKGROUND

The mechanism by which hypophosphataemia develops following kidney transplantation remains debated, and limited research is available regarding risk factors. This study aimed to assess the association between recipient and donor variables, and the severity of post-transplantation hypophosphataemia.

METHODS

We performed a single-centre retrospective observational study. We assessed the association between demographic, clinical and biochemical variables and the development of hypophosphataemia. We used linear regression analysis to assess association between these variables and phosphate nadir.

RESULTS

87.6% of patients developed hypophosphataemia. Patients developing hypophosphataemia were younger, had a shorter time on renal replacement therapy, were less likely to have had a parathyroidectomy or to experience delayed graft function, were more likely to have received a living donor transplant, from a younger donor. They had higher pre-transplantation calcium levels, and lower alkaline phosphatase levels. Receipt of a living donor transplant, lower donor age, not having had a parathyroidectomy, receiving a transplant during the era of tacrolimus-based immunosuppression, not having delayed graft function, higher pre-transplantation calcium, and higher pre-transplantation phosphate were associated with lower phosphate nadir by multiple linear regression.

CONCLUSIONS

This analysis demonstrates an association between variables relating to better graft function and hypophosphataemia. The links with biochemical measures of mineral-bone disease remain less clear.

Prevalence and clinical correlates of hyperkalemia in stable kidney transplant recipients

Although hyperkalemia (HK) is often associated with adverse clinical outcomes in renal patients, few studies are available in the setting of kidney transplantation. Therefore, we evaluated prevalence and clinical correlates of HK in stable kidney transplant recipients (KTRs) on standard of care immunosuppressive therapy. We studied 160 stable KTRs (post-transplant vintage 46.6 ± 16.6 months), most of whom (96.2%) on calcineurin inhibitor (CNI)-based immunosuppressive therapy. HK was defined as plasma potassium levels above 5 mEq/L, confirmed in two consecutive samples. Office blood pressure was measured, and renal graft function was expressed by estimated glomerular filtration rate (eGFR), calculated according to the CKD-EPI formula. HK prevalence was 8.8%, and plasma K above 5.5 mEq/L was found in 2.5% of all KTRs. In the univariate logistic regression analysis HK was significantly associated with serum urea concentration (OR 1.03, 95% CI 1.01-1.05 for each 1 mg/dL increase), tCO₂ (OR 0.77, 95% CI 0.66-0.90 for each 1 mmol/L increase), the presence of arterial hypertension (OR 4.01, 95% CI 1.3-12.64), the use of RAAS inhibitors (OR 5.26, 95% CI 1.6-17.7), and eGFR less than 30 ml/min/1.73 m² (OR 7.51, 95% CI 2.37-23.77). By multivariable backward stepwise regression analysis, the presence of metabolic acidosis (OR 0.83, 95% CI 0.69-0.99, P = 0.04), arterial hypertension (OR 4.65 95% CI 1.01-17.46 P = 0.03), and to be administered RAAS inhibitors (OR 6.11, 95% CI 1.03-25.96 P = 0.03) remained significantly associated with HK. We conclude that in stable KTRs the prevalence of HK is about 9%, slightly lower than previously reported. Moreover, it is not associated with eGFR, but with metabolic acidosis, arterial hypertension, and the use of RAAS inhibitors.

Regional Citrate Anticoagulation during Double-Filtration Plasmapheresis in Kidney Transplant Recipients: A Single-Center Retrospective Cohort Study

INTRODUCTION

Double-filtration plasmapheresis (DFPP) may be used for immunomodulation in kidney transplant (KTx). While DFPP reduces plasma product exposure, risk of circuit clotting merits adequate anticoagulation. Regional citrate anticoagulation (RCA) avoids the risks of systemic anticoagulation, but a protocol for RCA-DFPP is not previously widely described.

METHODS

We conducted a single-center retrospective cohort study involving adult (≥21 years old) KTx recipients who underwent RCA-DFPP from 2018 to 2020 to investigate efficacy and safety for an RCA protocol during DFPP in KTx recipients.

RESULTS

Fifty-one (85%) of 60 RCA-DFPP sessions in 17 patients completed without circuit clotting. Circuit clotting was associated with high post-filter ionized calcium (28 vs. 3.7%, odds ratio 10.1, 95% CI 1.1-89.4, p = 0.037). Hypo- and hypercalcemia developed in 5 (8.3%) and 8 (13.3%) sessions, respectively, but no adverse effects were noted despite severe hypocalcemia in one. There was no significant change in pre- and post-RCA-DFPP sodium, bicarbonate, albumin, and platelet levels. With regards DFPP procedure, prolongation of prothrombin time (PT) and activated partial thromboplastin time (aPTT) was observed following 38 (64.4%) and 12 (20.3%) sessions, respectively. Severely prolonged (>1.5 × upper limit normal) PT and aPTT were recorded in 2 sessions each. Expectedly, hypofibrinogenemia developed after 31 (51.7%) sessions: including 4 (6.7%) severe hypofibrinogenemia (<0.5 g/L). Two patients developed bleeding requiring blood product transfusion. The median total volume of fluids administered per session was 1.495 (1.373-1.612) L; post-RCA-DFPP significant weight gain of 0.5 (0-1.25) kg was noted. Diuretic was commenced or dose increased following 20 (33.3%) sessions for fluid balance management.

DISCUSSION/CONCLUSION

Protocol-based RCA for DFPP is feasible and safe in KTx recipients. However, DFPP-related coagulopathy can develop consequent to treatment; caution should be exercised for patients with bleeding risk. Close monitoring and management of the patients' electrolytes, especially hypocalcemia and hypomagnesemia, and fluid status is recommended.

Novel approaches to management of hyperkalaemia in kidney transplantation

PURPOSE OF REVIEW

Medications used frequently after kidney transplantation, including calcineurin inhibitors, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, beta blockers and antimicrobials, are considered the leading culprit for posttransplant hyperkalaemia in recipients with a well functioning allograft. Other risk factors include comorbidities such as diabetes, hypertension and heart failure; and consumption of a potassium-enriched diet. We review the mechanisms for hyperkalaemia following kidney transplantation that are addressed using nonpharmacological and pharmacological interventions. We also discuss emerging therapeutic approaches for the management of recurrent hyperkalaemia in solid organ transplantation, including newer potassium binding therapies.

RECENT FINDINGS

Patiromer and sodium zirconium cyclosilicate are emerging potassium binders approved for the treatment of hyperkalaemia. Patiromer is a polymer that exchanges potassium for calcium ions. In contrast, sodium zirconium cyclosilicate is a nonpolymer compound that exchanges potassium for sodium and hydrogen ions. Both agents are efficacious in the treatment of chronic or recurrent hyperkalaemia and may result in fewer gastrointestinal side effects than older potassium binders such as sodium polystyrene sulfonate and calcium polystyrene sulfonate. Large-scale clinical studies have not been performed in kidney transplant patients. Patiromer may increase serum concentrations of tacrolimus, but not cyclosporine. Sodium zirconium cyclosilicate does not appear to compromise tacrolimus pharmacokinetics, although it may have a higher sodium burden.

SUMMARY

Patiromer and sodium zirconium cyclosilicate may be well tolerated options to treat asymptomatic hyperkalaemia and have the potential to ease potassium dietary restrictions in kidney transplant patients by maintaining a plant-dominant, heart-healthy diet. Their efficacy, better tolerability and comparable cost with respect to previously available potassium binders make them an attractive therapeutic option in chronic hyperkalaemia following kidney transplantation.