FC 122BONE DENSITOMETRY IN RENAL TRANSPLANTED PATIENTS
Authors: Ferreira Ana Carina , Mendes Marco , Silva Cecília , Cotovio Patrícia , Aires Inês , Navarro David , Caeiro Fernando , Salvador Rute , Correia Bruna , Cabral Guadalupe , Nolasco Fernando , Ferreira Manuel Anibal A 
Published: May 2021

Abstract

Background and Aims
Renal transplant and associated immunosuppression can influence bone volume. The aim of this study was to analyze the relations between bone biopsy data and levels of bone-related molecules [phosphorus (Pi), Calcium (Ca), Magnesium (Mg), parathyroid hormone (PTH), bone alkaline phosphatase (bAP), calcitonin, vitamin D (vitD), alpha-klotho, fibroblast grow factor (FGF) 23, sclerostin], obtained 1-year after transplantation with bone densitometry findings in the same time point in renal transplanted patients.

Method
We performed a prospective cohort study of a consecutive sample of de novo single renal transplanted patients in our unit. At inclusion, demographic, clinical and transplant-related data were collected, X-ray of the pelvis and hands (Adragão score) and echocardiographic findings were recorded. All patients were submitted to a laboratorial evaluation and a bone biopsy at baseline. Patients were followed for 12 months, after which performed laboratorial evaluation, 2nd bone biopsy, echocardiogram, X-ray of pelvis and hands, bone densitometry (DXA) and non-contrast cardiac CT. For this report we use the information of the 2nd analysis: laboratorial information, bone histology information, as well the densitometry evaluation. Continuous variables were presented as medians and categorical variables as frequencies. Associations between variables were performed using Wilcoxon rank-sum test, Fisher exact test, Kruskal Wallis rank test or Spearman correlation test. Multivariate analysis was performed using linear regression models. STATA software was used and p &lt; 0.05 was considered statistically significant.

Results
We recruited 84 patients and, at the end of 12 months, we performed a 2nd evaluation in 69 patients. Median age 53 years, 48 men, 53 caucasian (78.8%), median BMI 24.6, median dialysis vintage 55 months. Patients had a median cumulative steroid dose of 5692.5 mg. Analyzing bone biopsies, we found that 28 patients had adynamic bone disease; 6 had hyperparathyroid bone disease; 2 had osteomalacia and 3 other abnormal mineralization; 8 patients presented only with osteoporosis. There was no significant difference between bone volume / total volume pre transplant (18%) and 1 year after transplantation (19%). Using DXA technique, 14 patients were classified has having osteoporosis, and all those had low volume at the bone biopsy. Nevertheless, in 4 patients low bone turnover was also present. The positive predictive value dropped from 100% to 57%, if we add the other abnormalities of bone, in addiction to the volume. DXA exam wasn’t a good tool to detect a normal bone volume, as the negative predicted value dropped from 78% (normal volume, irrespective of turnover and mineralization) to 37% (normal bone biopsy). Nevertheless, overall bone volume assessed by a bone biopsy correlated well with densitometry findings.

Conclusion
DXA exam isn’t a good tool to identify the bone quality. Nevertheless, once osteoporosis is detected the probability of the patient having low bone volume is high, but we still need a bone biopsy in order to exclude mineralization or turnover deviations.