Prevalence of Osteoporosis, Osteopenia, and Vertebral Fractures in Long-Term Renal Transplant Recipients

Clinical predictors of incipient vertebral fractures and bone mineral density in kidney transplant patients

PURPOSE

Kidney transplant recipients are prone to metabolic bone diseases and consequent fractures. This study aimed to evaluate the incidence of incipient vertebral fractures, osteopenia, osteoporosis, and the clinical factors associated with incipient vertebral fractures in a group of kidney transplant patients.

METHODS

Two hundred sixty-four patients (F/M 124/140, 45.3 ± 13 years) who had undergone kidney transplantation in tertiary care centers were included. Vertebral fractures were assessed semiquantitatively using conventional thoracolumbar lateral radiography in 202 of the patients.

RESULTS

Vertebral fractures were observed in 56.4% (n = 114) of the study group. The frequency of osteoporosis was 20.0% (53 of 264 patients), and osteopenia was 35.6% (94 of 264 patients). Bone mineral density (BMD) levels were in the normal range in 40.3% (n = 46) of the subjects with vertebral fractures. It was in the osteoporotic range in 20.1% (n = 23) and the osteopenic range in 40.3% (n = 46). Vertebral fractures were associated with age, duration of hemodialysis, BMI, and femoral neck Z score (R² 37.8%, p = 0.027).

CONCLUSION

As incipient vertebral fractures can be observed in patients with normal BMD levels in kidney transplant recipients, conventional X-ray screening for vertebral fractures may be beneficial for a proper therapy decision of metabolic bone disease in kidney transplant recipients.

Bone Mineral Density Changes in Long-Term Kidney Transplant Recipients: A Real-Life Cohort Study of Native Vitamin D Supplementation

Vitamin D insufficiency has been associated with reduced bone mineral density (BMD) in kidney transplant patients (KTRs). However, the efficacy of vitamin D supplementation on BMD remains poorly defined, especially for long-term KTRs. We aimed to investigate the effect of native vitamin D supplementation on the BMD of KTRs during a 2-year follow-up. Demographic, clinical, and laboratory data were collected. BMD was evaluated with standard DEXA that was performed at baseline (before vitamin D supplementation) and at the end of study period. BMD was assessed at lumbar vertebral bodies (LV) and right femoral neck (FN) by a single operator. According to WHO criteria, results were expressed as the T-score (standard deviation (SD) relative to young healthy adults) and Z-score (SD relative to age-matched controls). Osteoporosis and osteopenia were defined as a T-score ≤ -2.5 SD and a T-score < -1 and a > -2.5 SD, respectively. Based on plasma levels, 25-OH-vitamin D (25-OH-D) was supplemented as recommended for the general population. Data from 100 KTRs were analyzed. The mean study period was 27.7 ± 3.4 months. At study inception, 25-OH-D insufficiency and deficiency were recorded in 65 and 35 patients. At the basal DEXA, the percentage of osteopenia and osteoporosis was 43.3% and 18.6% at LV and 54.1% and 12.2% at FN, respectively. At the end of the study, no differences in the Z-score and T-score gains were observed. During linear mixed model analysis, native vitamin D supplementation was found to have a negative nitration with Z-score changes at the right femoral neck in KTRs (p < 0.05). The mean dose of administered cholecalciferol was 13.396 ± 7.537 UI per week; increased 25-OH-D levels were found (p < 0.0001). Either low BMD or 25-OH-vitamin D concentration was observed in long-term KTRs. Prolonged supplementation with 25-OH-D did not modify BMD, Z-score, or T-score.

Bone Mineral Density and Aortic Calcification: Evidence for a Bone-vascular Axis After Kidney Transplantation

BACKGROUND

Chronic kidney disease mineral and bone disorders (CKD-MBD) and vascular calcification are often seen in kidney transplantation recipients (KTR). This study focused on the bone-vascular axis hypothesis, the pathophysiological mechanisms driving both bone loss and vascular calcification, supported by an association between lower bone mineral density (BMD) and higher risk of vascular calcification.

METHODS

KTR referred for a dual-energy X-ray absorptiometry procedure within 6 mo after transplantation were included in a cross-sectional study (2004-2014). Areal BMD was measured at the proximal femur, and abdominal aortic calcification (AAC) was quantified (8-points score) from lateral single-energy images of the lumbar spine. Patients were divided into 3 AAC categories (negative-AAC: AAC 0; low-AAC: AAC 1-3; and high-AAC: AAC 4-8). Multivariable-adjusted multinomial logistic regression models were performed to study the association between BMD and AAC.

RESULTS

We included 678 KTR (51 ± 13 y old, 58% males), 366 (54%) had BMD disorders, and 266 (39%) had detectable calcification. High-AAC was observed in 9%, 11%, and 25% of KTR with normal BMD, osteopenia, and osteoporosis, respectively (P < 0.001). Higher BMD (T-score, continuous) was associated with a lower risk of high-AAC (odds ratio 0.61, 95% confidence interval 0.42-0.88; P = 0.008), independent of age, sex, body mass index, estimated glomerular filtration rate, and immunosuppressive therapy. KTR with normal BMD were less likely to have high-AAC (odds ratio 0.24, 95% confidence interval 0.08-0.72; P = 0.01).

CONCLUSIONS

BMD disorders are highly prevalent in KTR. The independent inverse association between BMD and AAC may provide evidence to point toward the existence, while highlighting the clinical and epidemiological relevance, of a bone-vascular axis after kidney transplantation.

Low bone density, vertebral fracture and FRAX score in kidney transplant recipients: A cross-sectional cohort study

Background

Kidney transplantation (KT) recipients are at increased risk of low bone density (LBD) and fractures. In this retrospective study, we investigated bone mineral density (BMD), vertebral fractures, calculated risk for major osteoporotic fractures (MOF), and hip fractures in the KT recipients.

Patients-method

Patients who completed at least one year after KT were included in the analysis. Demographic, clinical, and laboratory data were recorded. Measurements of BMD were performed by dual-energy X-ray absorptiometry. Vertebral fractures were assessed using semi-quantitative criteria with conventional radiography. The ten-year risk for MOF and hip fracture were calculated using the FRAX@ tool with BMD.

Results

One hundred fifty-three KT recipients were included in the study. The population included 77 women. The mean age at evaluation was 46,5±11,9 years. Seventy-eight (50.9%) patients had normal femoral neck BMD while osteoporosis and osteopenia at the femoral neck were present in 12 (7.8%) and 63 (41.1%) of the patients, respectively. Age at evaluation was the risk factor for LBD (OR 1.057; 95% CI 1.024–1.091; p = 0.001). In female KT recipients, LBD was principally affected by menopausal status whereas in males, mammalian target of rapamycin (mTOR) inhibitor use and lower BMI levels were the risk factors. The prevalent vertebral fracture was found in 43.4% of patients. In multivariate analysis, only steroid use (OR 0.121; 95% CI 0.015–0.988; p = 0.049) was found to be associated with prevalent fracture. Among all KT recipients, 1.9% had a high MOF probability (≥20% risk of fracture), and 23.5% had high hip fracture probability (≥3% risk of hip fracture) according to FRAX.

Conclusion

Exploring the prevalence of LBD and vertebral fracture and the risk factors would help clinicians to modify long-term follow-up strategies. Furthermore, the high hip fracture risk probability in our cohort suggested that there is a need for longitudinal studies to confirm the validity of the FRAX tool in the transplant population.

Fractures and Subsequent Graft Loss and Mortality among Older Kidney Transplant Recipients

OBJECTIVES

Older adults who undergo kidney transplantation (KT) are living longer with a functioning graft and are at risk for age-related adverse events including fractures. Understanding recipient, transplant, and donor factors and the outcomes associated with fractures may help identify older KT recipients at increased risk. We determined incidence of hip, vertebral, and extremity fractures; assessed factors associated with incident fractures; and estimated associations between fractures and subsequent death-censored graft loss (DCGL) and mortality.

DESIGN

This was a prospective cohort study of patients who underwent their first KT between January 1, 1999, and December 31, 2014.

SETTING

We linked data from the Scientific Registry of Transplant Recipients to Medicare claims through the US Renal Data System.

PARTICIPANTS

The analytic population included 47 815 KT recipients aged 55 years or older.

MEASUREMENTS

We assessed the cumulative incidence of and factors associated with post-KT fractures (hip, vertebral, or extremity) using competing risks models. We estimated risk of DCGL and mortality after fracture using adjusted Cox proportional hazards models.

RESULTS

The 5-year incidence of post-KT hip, vertebral, and extremity fracture for those aged 65 to 69 years was 2.2%, 1.0%, and 1.7%, respectively. Increasing age was associated with higher hip (adjusted hazard ratio [aHR] = 1.37 per 5-y increase; 95% confidence interval [CI] = 1.30-1.45) and vertebral (aHR = 1.31; 95% CI = 1.20-1.42) but not extremity (aHR = .97; 95% CI = .91-1.04) fracture risk. DCGL risk was higher after hip (aHR = 1.34; 95% CI = 1.12-1.60) and extremity (aHR = 1.30; 95% CI = 1.08-1.57) fracture. Mortality risk was higher after hip (aHR = 2.31; 95% CI = 2.11-2.52), vertebral (aHR = 2.80; 95% CI = 2.44-3.21), and extremity (aHR = 1.85; 95% CI = 1.64-2.10) fracture.

CONCLUSION

Our findings suggest that older KT recipients are at higher risk for hip and vertebral fracture but not extremity fracture; and those with hip, vertebral, or extremity fracture are more likely to experience subsequent graft loss or mortality. These findings underscore that different fracture types may have different underlying etiologies and risks, and they should be approached accordingly. J Am Geriatr Soc 67:1680-1688, 2019.

Changes in bone mineral density after kidney transplantation: 2-year assessment of a French cohort

INTRODUCTION

In renal transplant patients, bone loss may be related to the drugs patients are taking but also to their past history of chronic kidney disease. The purpose of this study was to assess changes in BMD 2 years after an initial assessment (performed 9 months post transplantation) and the factors associated with these changes.

METHODS

This longitudinal study included patients who had undergone a renal transplantation between 2005 and 2011, and who were followed up at the Lille Regional University Hospital. Patients were included if they had a first bone evaluation (including bone densitometry, spine X-rays and biological assessment) and at least another BMD assessment. The first assessment was performed on average 9 months post transplantation. A second assessment was performed at 2 years.

RESULTS

Two hundred fifty-nine out of 366 patients satisfied the inclusion criteria. The population included 96 women. Mean age at transplantation was 49.7 ± 12.1 years. Mean duration of dialysis was 3.2 ± 3.3 years. For 75 patients (29.0%), corticosteroid treatment was discontinued 7 days after transplantation without subsequent resumption during follow-up. Vertebral fractures assessed by X-rays at baseline were found in 28 patients (10.8%). According to the WHO classification, 106 patients (40.9%) patients had osteoporosis and 111 patients (42.8%) had osteopenia at the first assessment. Oral bisphosphonates were prescribed for 95 patients. The decision to prescribe bisphosphonates was taken jointly by rheumatologists and nephrologists based on BMD assessment, past history of fracture and corticosteroid management. In all patients, BMD gains at the second evaluation (2.2 ± 0.79 years) compared with baseline were significant (3.9 ± 6.6, 2.6% ± 7.6, 3.0 ± 7.2% at the lumbar spine, femoral neck and total hip respectively; p < 0.0001). The difference in gain between bisphosphonate-treated and untreated patients was significant (+ 5.0 ± 0.8% (p < 0.0001), + 2.5 ± 1.0% (p = 0.01) and + 2.7 ± 0.9% (p < 0.01) at the lumbar spine, femoral neck and total hip respectively. The patients who benefited early corticosteroid discontinuation had higher gains in BMD at the lumbar spine (+ 2.1 ± 0.9%; p = 0.02) and total hip (+ 2.0 ± 1.0%; p = 0.04) compared to those for whom corticosteroid therapy was maintained. Stepwise regression analysis (patients without bisphosphonates) showed associations between change in BMD (femoral neck) and duration of corticosteroid therapy, bone alkaline phosphatase level at baseline, and absence of vertebral fracture. No correlation was found between change in BMD and duration of dialysis or renal function.

CONCLUSION

Kidney transplant recipients have an increased risk of bone fragility in the year following transplantation. Bisphosphonates and early corticosteroid discontinuation can improve BMD.

Lumbar Spine Fusion Surgery in Solid Organ Transplant Recipients Is Associated With Increased Medical Complications and Mortality

STUDY DESIGN

Retrospective database review.

OBJECTIVE

To characterize the outcomes of solid organ transplant (SOT) patients after one- or two-level lumbar fusion surgery.

SUMMARY OF BACKGROUND DATA

Over the past decade advances in SOT patients have improved graft survival. As such, this patient population is increasingly eligible for elective surgery such as lumbar fusion procedures to improve mobility and quality of life. However, the outcomes of spine surgery in this population are not well defined.

METHODS

Data from the full 100% Medicare sample between 2005 and 2014 were used for the study. Patients were included if they had an elective one- or two-level lumbar spine fusion and previous history of renal, heart, liver, or lung SOT patients during this period. SOT patients were compared to non-SOT patients with respect to baseline characteristics, 90-day medical complications, 1-year rate of revision surgery, and 1-year mortality.

RESULTS

There were 961 patients in the transplant cohort and 258,342 in the non-SOT cohort. Seventy-seven percent of the SOT patients had prior renal transplant. SOT patients had a longer length of stay (P < 0.001), and a higher 30-day readmission rate compared to non-SOT patients (P =  < 0.001). In addition, SOT patients experienced a 23.8% rate of 90-day postoperative major medical complications and 3.0%, 1-year mortality, significantly larger than respective rates in the control population (P < 0.001). One-year infection, revision surgery rates, and wound dehiscence were not significantly different between the two cohorts.

CONCLUSION

Spine surgery is associated with significant medical complications and 1-year mortality in the SOT population. Although there may be a substantial benefit from lumbar fusion in the SOT population, judicious patient selection is of paramount importance.

LEVEL OF EVIDENCE

3.

Serum phosphorus levels and fracture following renal transplantation

PURPOSE

Increased fracture rates are observed in renal transplant recipients (RTRs) compared with the general population. Risk factors include age, diabetes, dialysis vintage, immunosuppression and mineral and bone disorders.¹ Low serum phosphorus levels occur post-transplantation; however, its relationship with fracture risk has not been evaluated. The purpose of this study was to evaluate risk factors for fracture in RTRs at a single tertiary referral centre.

METHODS

A retrospective cross-sectional analysis of 146 patients (75 M, 71 F) who had been referred for dual energy X-ray densitometry (DXA) post-renal transplantation was performed. Aetiology of end stage kidney disease (ESKD), duration of dialysis, parathyroidectomy history, immunosuppression regimen, bone mineral density (BMD), biochemistry and fractures were documented. Statistical analyses included univariable and multivariable regression.

RESULTS

The mean age of patients was 54 years and mean time post-transplantation 6.7 years. A total of 79 fractures occurred in 52 patients (35%), with 40 fractures occurring post-transplantation. Ankle/foot fractures were most common (48%). Lower serum phosphorus levels and declining femoral neck (FN) T-score and were associated with fractures in both univariable and multivariable regression analyses after adjusting for age, gender, weight, estimated glomerular filtration rate and pre-transplant history of fracture (P=.011 and P=.042 respectively). The relationship between serum phosphorus and fracture remained significant independent of FN T-score, parathyroid hormone levels, parathyroidectomy status and prednisolone use.

CONCLUSION

Fracture was common post-renal transplantation. Lower serum phosphorus levels and declining FN T-scores were associated with fractures. The mechanism of this previously unreported observation requires further evaluation in prospective studies.

Bone Disease and Serum Fibroblast Growth Factor-23 Levels in Renal Transplant Recipients

BACKGROUND

Posttransplantation bone disease develops commonly and results in important complications. In this study, we aimed to investigate the relationship between bone diseases and serum fibroblast growth factor-23 (FGF-23) in renal transplant recipients.

METHODS

This study was conducted in 106 kidney transplant recipients (KTrs; group G1) and 30 patients with chronic kidney disease (group G2). Patients with fever, heart failure, angina pectoris, acute renal failure, malignant disease, or any gastrointestinal disease were excluded. KTrs were treated with triple immunosuppressive drugs including glucocorticoids. Complete blood count (CBC), blood urea nitrogen (BUN), creatinine, glomerular filtration rate (GFR, Modification of Diet in Renal Disease [MDRD] formula), lipid profile, calcium (Ca), phosphorous (P), parathormone (PTH), 25OHD3, serum levels of tacrolimus/cyclosporine, and intact FGF-23 were measured. Bone mineral density (BMD) was measured with dual energy X-ray absorptiometry.

RESULTS

The mean patient age was 40.1 ± 11.1 years and 39.2 ± 11.3 years in G1 and G2, respectively (P > .05). In G1 and G2, 76 and 15 patients were male, respectively. Compared with the G2 patients, G1 patients had lower body mass index (BMI), serum glucose levels, P, Mg, and Ca·P (P < .05 for all). T scores of the lumbar vertebrae/femur were -1.82 ± 0.99/-1.34 ± 0.89 and -1.13 ± 1.34/-0.51 ± 1.18 in G1 and G2 patients, respectively (P < .05 for all). The incidences of osteopenia/osteoporosis in the lumbar spine and femur were 50.9%/27.4% and 57.5%/10.4% in G1 and 16.6%/23.3%, and 40%/3.3% in G2. There were positive correlations between BMD and BMI, the time elapsed after renal transplantation, and GFR. In our study, a statistically significant relationship was found between lipid parameters and BMD, PTH, and 250HD3 levels, as well as use of corticosteroid and calcineurin inhibitors (P < .05 for all). In G1 and G2, BMD of the lumbar spine in patients with serum creatinine >1.5 mg/dL was lower than that in patients with serum creatinine <1.5 mg/dL.

CONCLUSION

The association between age and BMD was found only in the femur of KTrs. No relationship was observed between serum FGF-23 levels and BMD values. In both groups, the BMD T score of the lumbar spine was lower compared to the BMD T score of the femur and in patients with serum creatinine >1.5 mg/dL. In long-term follow-up of renal transplantation by as much as 58 months, the incidence of bone disease such as osteoporosis/osteopenia was as high as 67% and was also higher than that of nontransplant patients with similar GFR. In addition to decreased renal function, dyslipidemia, inflammation, and continuing hypophosphatemia were also accompanied by decreased BMD as in cardiovascular disease in KTrs.

Understanding Bone Damage After Kidney Transplantation: A Retrospective Monocentric Cross Sectional Analysis

BACKGROUND

Kidney transplantation (KT) immunosuppression may induce bone tissue damage with bone mineral density (BMD) loss increasing bone fractures risk. Steroid therapy is considered the major player, but others factors are still under review.

PATIENTS AND METHODS

We designed an observational retrospective cohort study to evaluate bone damage after KT. The prevalence of osteopenia, osteoporosis, bone fractures, and the associated risk factors were investigated. The following parameters were recorded before transplantation and at the last follow-up: demographic indexes, cumulative steroid dose (CSD), dialytic and transplantologic age, previous nephropathy, femoral and lumbar BMD, fractures, immunosuppressors, calcemia, phosphoremia, rejection episodes, estimated glomerular filtration rate, and parathyroid hormone and vitamin D levels. Stata software (Stata Corporation, College Station, Texas, United States) was used for the statistical analysis, to perform the Fisher's exact test, Kruskal-Wallis test, Student t test, as well as univariate and multivariate analyses.

RESULTS

The analyzed cohort was composed of 297 patients (65.3% males and 34.7% females). Sixty percent of KT patients had normal BMD, 24% had osteopenia, and 15% had osteoporosis. Twelve percent were victims of bone fractures (8.4% minor, 2% femoral, and 1.7% vertebral). A significant correlation (P <.05) was observed for both osteopenia and osteoporosis with menopause, transplantologic age, CSD, previous glomerulonephritis, and mammalian target of rapamycin (mTOR) inhibitors treatment (imTOR).

CONCLUSION

This study confirms the correlation between CSD (both before and after transplantation) and post-transplantation bone damage. It also shows that a large fraction of these patients had normal BMD related with a low steroid dose in our protocols. This correlation between imTOR assumption and osteoporosis deserves attention and warrants further in vitro analyses to be performed.

Bone fractures and lumbar mineral density after renal transplantation. A long-term cross-sectional study

BACKGROUND

The purpose of this work was to investigate the association of vertebral and peripheral fractures 10 yr after grafting with bone metabolic markers and body mass density (BMD).

PATIENTS AND METHODS

One hundred thirty-eight recipients with stable graft function were included in a cross-sectional study. Graft function, biochemical mineral metabolism markers and body mass density (DEXA) were measured. Vertebral fractures were assessed by a semiquantitative analysis of lateral spine X-ray exam.

RESULTS

At the time of the study, intact parathyroid hormone levels were 127.5 ± 78.4 pg/mL and serum calcidiol 20.4 ± 9.3 ng/mL. DEXA showed osteopenia in 47% and osteoporosis in 23% at lumbar spine, 51% and 14% at femoral neck, and 53% and 8% at trochanter. Eighty-five recipients presented vertebral fractures, 69 mild and 16 moderate/severe fractures. In the multivariate analysis, vertebral fractures were associated with older age (p = 0.010), length of follow-up (p = 0.022) and trochanter T-score (p = 0.038). Twenty-three patients presented peripheral fractures and 19 of them also had vertebral fractures. Patients with peripheral fractures were younger, mostly women and had lower BMD.

CONCLUSIONS

Vertebral fractures were associated with lower BMD at trochanter. Most fractures were mild and were several times more frequent than in general population. Their clinical significance needs to be determined.

Long-term changes in bone mineral density in kidney transplant recipients

BACKGROUND

Alterations in bone mineral metabolism occur when kidney function declines and often continue after transplantation. We investigated long-term changes in bone mineral density (BMD) among kidney transplant recipients undergoing routine clinical BMD monitoring and management.

METHODS

We identified adults receiving a kidney transplant in the province of Manitoba, Canada (1996-2011) who had greater than or equal to 2 posttransplant dual energy X-ray absorptiometry examinations. Bone mineral density was expressed as Z scores (standard deviation above/below sex-matched and age-matched reference data). The main outcome was the change in BMD.

RESULTS

A total of 326 kidney transplant recipients were included (mean age, 45 years; 61% men). Recipients were followed up for an average of 8.2 years (766 follow-up dual energy X-ray absorptiometry measurements). At baseline (first scan; median, 0.5 years after transplantation), bone density was slightly below average for age and sex (mean Z scores: lumbar spine, -0.4 ± 1.6; femoral neck, -0.7 ± 1.1; total hip, -0.7 ± 1.1). At the second scan (mean, 2.7 years after first scan), mean bone density Z scores have increased (lumbar spine, -0.2 ± 1.6; femoral neck, -0.6 ± 1; total hip, -0.6 ± 1.1; matched, P < 0.01 at all sites). The only factor associated with a significant BMD change at all sites was osteoporosis treatment (BMD increase). Even after restricting the analysis to recipients who had not received osteoporosis treatment, final mean bone density (mean, 8.2 years after first scan) was average for age and sex (lumbar spine, +0.7 ± 1.6; femoral neck, -0.1 ± 1.1; total hip, 0.0 ± 1.1).

CONCLUSION

With routine BMD monitoring and management, posttransplant bone density typically remains stable or improves with mean values that are average for age and sex.

Is Klotho F352V Polymorphism the Missing Piece of the Bone Loss Puzzle in Renal Transplant Recipients?

BACKGROUND

Bone disorders are next to cardiovascular problems in frequency in renal transplant (RT) recipients. Reduction in 1,25-dihydroxycholecalciferol (1,25D) levels is among the reasons causing bone loss in these patients. Klotho (KL) serves as a co-receptor for fibroblast growth factor 23 (FGF23), and functions in vitamin D metabolism. KL polymorphisms have been identified in several studies, and phenylalanine to valine substitution at amino acid position 352 seemed to be important to KL function. We investigated KL F352V polymorphism and its relation with 1,25D levels in RT recipients.

METHODS

The study included 25 RT recipients (8 female, 17 male) and 26 (14 female, 12 male) healthy control subjects who were wild (FF) phenotypes in terms of KL F352V polymorphism. RT recipients with (FV, n = 11) and without (FF, n = 14) a heterozygote polymorphism were determined with high resolution DNA melting analysis of KL F352V polymorphism. Serum 1,25D levels were measured using the RIA method.

RESULTS

RT recipients with FV phenotype had significantly lower 1,25D levels (17.58 ± 18.38 pg/ml) compared to recipients with FF phenotype (44.91 ± 24.68 pg/ml) and control subjects (28.24 ± 12.13 pg/ml). 1,25D levels in RT recipients with FF phenotype were significantly higher than control subjects.

CONCLUSIONS

KL F352V polymorphism may increase the expression of FGF23 co-receptor, KL protein and thus may decrease renal expression of 1α-hydroxylase, and/or stimulate 24-hydroxylase in RT recipients. The resultant decrease 1,25D levels may participate in bone loss in these patients.

Osteoporosis after renal transplantation

Bone loss and fracture are serious sequelae of kidney transplantation, associated with morbidity, mortality and high economic costs. The pathogenesis of post-transplantation bone loss is multifactorial and complex. Pre-existing bone mineral disease is responsible for a significant part, but it is aggravated by risk factors emerging after renal transplantation with immunosuppressive agents being one of the key contributors. The decrease in bone mass is particularly prominent during the first 6-12 months after transplantation, continuing at a lower rate thereafter. Bone mineral density measurements do not predict bone histology and bone biopsy findings reveal heterogeneous lesions, which vary according to time after transplantation. Currently, vitamin D and bisphosphonates are the most extensively tested therapeutic agents against this accelerated bone loss in renal transplant recipients. Both of these agents have proven effective, but there is no evidence that they decrease fracture risk. More studies are needed to examine the complex pathophysiologic mechanisms implicated in this population, as well as the effects of different therapeutic interventions on bone disorders after kidney transplantation.

CKD-mineral and bone disorder management in kidney transplant recipients

Kidney transplantation, the most effective treatment for the metabolic abnormalities of chronic kidney disease (CKD), only partially corrects CKD-mineral and bone disorders. Posttransplantation bone disease, one of the major complications of kidney transplantation, is characterized by accelerated loss of bone mineral density and increased risk of fractures and osteonecrosis. The pathogenesis of posttransplantation bone disease is multifactorial and includes the persistent manifestations of pretransplantation CKD-mineral and bone disorder, peritransplantation changes in the fibroblast growth factor 23-parathyroid hormone-vitamin D axis, metabolic perturbations such as persistent hypophosphatemia and hypercalcemia, and the effects of immunosuppressive therapies. Posttransplantation fractures occur more commonly at peripheral than central sites. Although there is significant loss of bone density after transplantation, the evidence linking posttransplantation bone loss and subsequent fracture risk is circumstantial. Presently, there are no prospective clinical trials that define the optimal therapy for posttransplantation bone disease. Combined pharmacologic therapy that targets multiple components of the disordered pathways has been used. Although bisphosphonate or calcitriol therapy can preserve bone mineral density after transplantation, there is no evidence that these agents decrease fracture risk. Moreover, bisphosphonates pose potential risks for adynamic bone disease.

Risk of fractures after renal transplantation in the United States

BACKGROUND

Although it is known that the incidence of fracture events is increased in renal transplantation recipients, the timing and the factors associated with risk of fractures are less well understood. The objective of this study was to estimate the time to fracture in renal transplantation recipients and to determine whether risk was associated with patient and transplantation characteristics.

METHODS

Using the U. S. Renal Data System, we retrospectively studied 68,814 patients, who underwent renal transplantation between 1988 and 1998. Fractures were identified from International Classification of Diseases, Ninth Revision, Clinical Modification diagnosis codes in billing data. Time to first fracture was modeled during the first 5 years posttransplant using the Kaplan-Meier method and Cox proportional hazards models.

RESULTS

Of the patients who underwent transplantation, 22.5% developed a fracture within 5 years. Woman (hazard ratio [HR] 1.36, P<0.0001), patients older than 45 years of age (HR 1.14, P<0.0001) especially older than 65 years (HR 1.69, P<0.0001), and whites (HR 1.28, P<0.0001) were at increased risk of a fracture. Additionally, receipt of a deceased donor kidney (HR 1.30, P<0.0001), increased human leukocyte antigen mismatches (HR 1.09, P<0.014), diabetes (HR 1.88, P<0.0001), pretransplant dialysis (HR 1.08, P<0.0001), and an aggressive induction immunosuppression regimen (HR 1.14, P<0.0001) all significantly increased risk of fracture events during the first 5 years.

CONCLUSIONS

In addition to patient demographic features, donor factors, including suboptimal organ quality and the need for more intense immunosuppression, were associated with an increased risk of fractures during the first 5 years after a renal transplant.

Can DXA predict fractures in renal transplant patients?

Renal transplant patients have a high prevalence of osteopenia, osteoporosis and fractures. The aim of the study was to investigate whether dual-energy x-ray absorptiometry (DXA) is of value to predict fractures. In 1995-2007, 238 renal transplant patients underwent 670 DXA investigations. Osteopenia (46.0%), osteoporosis (13.9%) and absolute bone mineral density (BMD) (median 0.9, range 0.4-2.0 g/cm(2)) in the hip region were used to evaluate fracture risk. Data on fractures were collected at the occasion of each DXA, and a questionnaire was filled in by 191 patients at regular outpatient visits. Reported fractures were verified by consultation of medical records. In all, 46 patients had 53 fractures. Cumulative hazard of fracture was significantly different among normal BMD, osteopenia and osteoporosis in the hip (p < 0.0001). A Cox proportional hazard analysis also including age, gender and diabetic nephropathy showed significantly increased fracture risk for osteoporosis (3.5 times, CI 1.8-6.4, p = 0.0001) as well as for osteopenia (2.7 times, 1.6-4.6, p = 0.0003). A significantly increased risk was also found with absolute BMD estimates below the median. Osteopenia and an absolute bone density below 0.9 g/cm(2) in the hip region confer an increased risk of fracture.