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Serum phosphorus levels may predict fracture after renal transplantation

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May 8, 2017

Fracture after renal transplantation may be predicted by lower serum phosphorus levels and declining femoral neck T-scores, according to findings published in Clinical Endocrinology.

“Peripheral fractures affecting sites rich in cortical bone are common following renal transplantation and, currently, no consensus guidelines exist regarding optimal prevention, screening and management of bone health following renal transplantation,” the researchers wrote. “This is the first study to demonstrate that lower serum phosphorus levels post-renal transplantation had the strongest association with fracture.”

Ja s n a Aleksova, MBBS, of the department of endocrinology at Monash Health in Australia, and colleagues evaluated 146 adults (mean age, 54 years; 75 men) referred for DXA after renal transplantation to determine the risk for fractures. Mean time since the transplantation was 6.7 years. Researchers documented etiology of end-stage kidney disease, duration of dialysis, parathyroidectomy history, immunosuppression regimen, bone mineral density, biochemistry and fractures. Thirty-one percent of the women participants were postmenopausal.

Overall, there were 79 fractures among 52 participants; 40 of which occurred after transplantation. A history of fracture before transplantation was found in 12 participants. Mean time to fracture after transplant was 4 years, with 75% occurring within the first 5 years. Lower limb fractures were the most common type of fracture.

Estimated glomerular filtration rate was 54.94 mL/min/1.73 m2, adjusted calcium was 2.4 mmol/L, phosphorus was 1.1 mmol/L and alkaline phosphatase was 88.33 U/L at the time of DXA imaging.

BMD was measured at a median of 5.1 years after transplantation. Less than 5% of participants were referred for DXA imaging with a secondary indication, including hyperparathyroidism, postmenopausal state or history of hypogonadism or early menopause.

In a linear multivariable regression analysis adjusted for age, sex and weight, prednisolone use was associated with lower lumbar spine areal BMD (P = .035) but not with femoral neck or total body areal BMD. There was no association found between pre-existing diabetes, time on dialysis and parathyroidectomy status with any BMD parameter.

Compared with renal-transplant-only participants, those who underwent simultaneous pancreas and kidney transplantation were younger (P = .001), had a higher incidence of fracture (P = .017), a shorter duration of dialysis before transplantation (P = .006), higher eGFR (P < .001) and lower femoral neck (P = .011) and total body BMD values (P = .006).

Posttransplant fractures were associated with femoral neck BMD (OR = 1.57; 95% CI, 1.01-2.42) and femoral neck T-score (OR = 1.62; 95% CI, 1.02-2.59) in the multivariable logistic regression analysis adjusted for age, sex, weight, pre-transplant facture history and eGFR. Fracture after transplantation was associated lower serum phosphorus (P = .002), lower creatinine (P = .022) and higher adjusted calcium (P = .013); in the adjusted model, only phosphorus remained a significant predictor (OR = 2.64; 95% CI, 1.24-5.75).

“Although less predictive than phosphorus, monitoring of BMD at the [femoral neck] may be useful in stratifying fracture risk for renal transplant recipients,” the researchers wrote. “Abnormalities in phosphorus homeostasis are common in renal transplant recipients and may contribute to adverse skeletal outcomes. Following this novel finding, additional research examining the pathophysiology of phosphorus homeostasis and its contribution to skeletal fragility following renal transplantation is now required.” – by Amber Cox

Disclosure: The researchers report no relevant financial disclosures.

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