Clinical manifestations of hypercalcemia and hypophosphatemia after kidney transplantation

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.

What is the clinical relevance of deviant serum calcium and phosphate levels after pig-to-primate kidney xenotransplantation?

Experience from human renal allotransplantation informs us that disturbances in serum calcium and phosphate levels are relatively common. Post-transplant hypercalcemia is associated with an increased risk of recipient mortality, but not of graft loss or nephropathy, and post-transplant hyperphosphatemia with an increased risk of both recipient mortality and death-censored graft failure, but neither post-transplant hypocalcemia nor hypophosphatemia is associated with adverse outcome. Studies after pig-to-nonhuman primate kidney xenotransplantation have demonstrated consistent supranormal serum calcium and subnormal serum phosphate levels. If these trends in serum electrolyte levels were to occur following pig-to-human kidney xenotransplantation, the data from allotransplant studies would indicate an increased risk of recipient mortality (associated with hypercalcemia) but not of graft loss or nephropathy, and no adverse outcome from hypophosphatemia. Furthermore, some nonhuman primates are now surviving in a healthy state for longer than a year after life-supporting pig kidney transplantation, suggesting that chronic hypercalcemia and/or hypophosphatemia are not detrimental to long-term survival, and should not prevent clinical trials of pig kidney transplantation from being undertaken.

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.

Calcium and phosphate levels after kidney transplantation and long-term patient and allograft survival

Background

Non-traditional cardiovascular risk factors, including calcium and phosphate derangement, may play a role in mortality in renal transplant. The data regarding this effect are conflicting. Our aim was to assess the impact of calcium and phosphate derangements in the first 90 days post-transplant on allograft and recipient outcomes.

Methods

We performed a retrospective cohort review of all-adult, first renal transplants in the Republic of Ireland between 1999 and 2015. We divided patients into tertiles based on serum phosphate and calcium levels post-transplant. We assessed their effect on death-censored graft survival and all-cause mortality. We used Stata for statistical analysis and did survival analysis and spline curves to assess the association.

Results

We included 1525 renal transplant recipients. Of the total, 86.3% had hypophosphataemia and 36.1% hypercalcaemia. Patients in the lowest phosphate tertile were younger, more likely female, had lower weight, more time on dialysis, received a kidney from a younger donor, had less delayed graft function and better transplant function compared with other tertiles. Patients in the highest calcium tertile were younger, more likely male, had higher body mass index, more time on dialysis and better transplant function. Adjusting for differences between groups, we were unable to show any difference in death-censored graft failure [phosphate = 1.14, 95% confidence interval (CI) 0.92–1.41; calcium = 0.98, 95% CI 0.80–1.20] or all-cause mortality (phosphate = 1.10, 95% CI 0.91–1.32; calcium = 0.96, 95% CI 0.81–1.13) based on tertiles of calcium or phosphate in the initial 90 days.

Conclusions

Hypophosphataemia and hypercalcaemia are common occurrences post-kidney transplant. We have identified different risk factors for these metabolic derangements. The calcium and phosphate levels exhibit no independent association with death-censored graft failure and mortality.

Electrolyte and Acid-Base Disorders in the Renal Transplant Recipient

Kidney transplantation is the current treatment of choice for patients with end-stage renal disease. Innovations in transplantation and immunosuppression regimens have greatly improved the renal allograft survival. Based on recently published data from the Scientific Registry of Transplant recipients, prevalence of kidney transplants is steadily rising in the United States. Over 210,000 kidney transplant recipients were alive with a functioning graft in mid-2016, which is nearly twice as many as in 2005. While successful renal transplantation corrects most of the electrolyte and mineral abnormalities seen in advanced renal failure, the abnormalities seen in the post-transplant period are surprisingly different from those seen in chronic kidney disease. Multiple factors contribute to the high prevalence of these abnormalities that include level of allograft function, use of immunosuppressive medications and metabolic changes in the post-transplant period. Electrolyte disturbances are common in patients after renal transplantation, and several studies have tried to determine the clinical significance of these disturbances. In this manuscript we review the key aspects of the most commonly found post-transplant electrolyte abnormalities. We focus on their epidemiology, pathophysiology, clinical manifestations, and available treatment approaches.

Long-term clinical practice experience with cinacalcet for treatment of hypercalcemic hyperparathyroidism after kidney transplantation

Within this prospective, open-label, self-controlled study, we evaluated the long-term effects of the calcimimetic cinacalcet on calcium and phosphate homeostasis in 44 kidney transplant recipients (KTRs) with hypercalcemic hyperparathyroidism by comparing biochemical parameters of mineral metabolism between pre- and posttreatment periods. Results are described as mean differences (95% CIs) between pre- and posttreatment medians that summarize all repeated measurements of a parameter of interest between the date of initial hypercalcemia and cinacalcet initiation (median of 1.6 (IQR: 0.6-3.8) years) and up to four years after treatment start, respectively. Cinacalcet was initiated after 1.8 (0.8-4.7) years posttransplant and maintained for 6.2 (3.9-7.6) years. It significantly decreased total serum calcium (-0.30 (-0.34 to -0.26) mmol/L, P < 0.001) and parathyroid hormone levels (-79 (-103 to -55) pg/mL, P < 0.001). Serum levels of inorganic phosphate (Pi) and renal tubular reabsorption of phosphate to glomerular filtration rate (TmP/GFR) increased simultaneously (Pi: 0.19 (0.15-0.23) mmol/L, P < 0.001, TmP/GFR: 0.20 (0.16-0.23) mmol/L, P < 0.001). In summary, cinacalcet effectively controlled hypercalcemic hyperparathyroidism in KTRs in the long-term and increased low Pi levels without causing hyperphosphatemia, pointing towards a novel indication for the use of cinacalcet in KTRs.

Mineral metabolism in European children living with a renal transplant: a European society for paediatric nephrology/european renal association-European dialysis and transplant association registry study

BACKGROUND AND OBJECTIVES

Data on mineral metabolism in pediatric renal transplant recipients largely arise from small single-center studies. In adult patients, abnormal mineral levels are related to a higher risk of graft failure. This study used data from the European Society for Paediatric Nephrology/European Renal Association-European Dialysis and Transplant Association Registry to study the prevalence and potential determinants of mineral abnormalities, as well as the predictive value of a disturbed mineral level on graft survival in a large cohort of European pediatric renal transplant recipients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study included 1237 children (0-17 years) from 10 European countries, who had serum calcium, phosphorus, and parathyroid hormone measurements from 2000 onward. Abnormalities of mineral metabolism were defined according to European guidelines on prevention and treatment of renal osteodystrophy in children on chronic renal failure.

RESULTS

Abnormal serum phosphorus levels were observed in 25% (14% hypophosphatemia and 11% hyperphosphatemia), altered serum calcium in 30% (19% hypocalcemia, 11% hypercalcemia), and hyperparathyroidism in 41% of the patients. A longer time since transplantation was associated with a lower risk of having mineral levels above target range. Serum phosphorus levels were inversely associated with eGFR, and levels above the recommended targets were associated with a higher risk of graft failure independently of eGFR.

CONCLUSIONS

Abnormalities in mineral metabolism are common after pediatric renal transplantation in Europe and are associated with graft dysfunction.