Using vertebral bone densitometry to determine aortic calcification in patients with chronic kidney disease

A Novel Quantitative Computer-Assisted Score Can Improve Repeatability in the Estimate of Vascular Calcifications at the Abdominal Aorta

In CKD and in the elderly, Vascular Calcifications (VC) are associated to cardiovascular events and bone fractures. VC scores at the abdominal aorta (AA) from lateral spine radiographs are widely applied (the 0-24 semiquantitative discrete visual score (SV) being the most used). We hypothesised that a novel continuum score based on quantitative computer-assisted tracking of calcifications (QC score) can improve the precision of the SV score. This study tested the repeatability and reproducibility of QC score and SV score. In forty-four patients with VC from an earlier study, five experts from four specialties evaluated the data twice using a dedicated software. Test-retest was performed on eight subjects. QC results were reported in a 0-24 scale to readily compare with SV. The QC score showed higher intra-operator repeatability: the 95% CI of Bland-Altman differences was almost halved in QC; intra-operator R2 improved from 0.67 for SV to 0.79 for QC. Inter-observer repeatability was higher for QC score in the first (Intraclass Correlation Coefficient 0.78 vs. 0.64), but not in the second evaluation (0.84 vs. 0.82), indicating a possible heavier learning artefact for SV. The Minimum Detectable Difference (MDD) was smaller for QC (2.98 vs. 4 for SV, in the 0-24 range). Both scores were insensitive to test-retest procedure. Notably, QC and SV scores were discordant: SV showed generally higher values, and an increasing trend of differences with VC severity. In summary, the new QC score improved the precision of lateral spine radiograph scores in estimating VC. We reported for the first time an estimate of MDD in VC assessment that was 25% lower for the new QC score with respect to the usual SV score. An ongoing study will determine whether this lower MDD may reduce follow-up times to check for VC progression.

Aortic pulse wave velocity is greater in peritoneal dialysis patients with lower dual energy X-ray absorptiometry (DXA) femoral neck bone mineral density

BACKGROUND

Increased vascular stiffness is associated with low bone mineral density (BMD) in the general population, and both are risk factors for mortality. We wished to determine whether vascular stiffness is associated with BMD in peritoneal dialysis (PD) patients.

METHODS

We measured vascular stiffness by aortic pulse wave velocity (aPWV), BMD by dual electron absorptiometry (DXA) scanning, and body composition using bioimpedance.

RESULTS

We reviewed DXA scans in 125 PD patients, 56.8% male, mean age 64.4 ± 15.3 years, mean aPWV, 10.2 ± 2.6 m/s. We divided patients by aPWV (< 10 and > 10 m/s), and there were no statistical differences in patient demographics, body composition, PD adequacy, peritoneal and urinary calcium losses. On univariate analysis aPWV was negatively associated with total body T score (r = - 0.20, p = 0.037). On multivariable logistic regression patients with higher aPWV were prescribed fewer non-calcium containing phosphate binders, odds ratio (OR) 0.83, 95% confidence interval (CI) 0.70-0.99, p = 0.039, more had lower 25 hydroxy-vitamin D₃ concentrations < 50 ng/L (OR 0.34, CI 0.12-0.93, p = 0.035, and lower femoral BMD OR 0.03 (CI 0-0.3.4), p = 0.029, but there was no association with total or lumbar spine BMD.

CONCLUSION

Our study reinforces the hypothesis of a link between bone disease and vascular disease in dialysis patients. As patients with higher aPWV were prescribed fewer non-calcium containing phosphate binders and fewer had higher 25 hydroxy-vitamin D₃ concentrations, then this raises the possibility that differences in clinical practice and drug prescribing may help to reduce vascular stiffness, which will require testing in future trials.

Fractional excretion of phosphorus and vascular calcification in stage 3 chronic kidney disease

The role of renal excretion of Pi in relation to vascular calcification (VC) in patients in the early stages of chronic kidney disease (CKD) is controversial. Thus, we determine the relation between fractional excretion of phosphorus (FEP) and VC, measured using two methods in a cross-sectional study of patients with stage 3 CKD. We recorded demographic data, anthropometry, comorbidities and active treatment. We measured 24-hour urine FEP and, in serum, measured fibroblast growth factor 23 (FGF23), α-Klotho, intact parathyroid hormone (iPTH), calcium and phosphorus. VC was measured by lateral abdominal radiography (Kauppila index (KI)) and CT of the abdominal aorta (measured in Agatston units). In 57% of subjects, abnormal VC was present when measured using CT, and in only 17% using lateral abdominal radiography. Factors associated with VC using CT were age, cardiovascular risk factors, vascular comorbidity, microalbuminuria and levels of FGF23, phosphorus and calcium x phosphorus product (CaxP); although only age (OR 1.25, 95% CI 1.11 to 1.41), smoking (OR 21.2, CI 4.4 to 100) and CaxP (OR 1.21, CI 1.06 to 1.37) maintained the association in a multivariate analysis. By contrast, only age (OR 1.35, 95% CI 1.07 to 1.74), CaxP (OR 1.14, CI 1.13 to 1.92) and FEP (OR 1.07,95% CI 1004 to 1.14) were associated with abnormal VC in the lateral abdominal radiography. In conclusion, in patients with stage 3 CKD, the detection of VC by abdominal CT is more sensitive than conventional X-rays. Moreover, CaxP is associated with cardiovascular risk factors and vascular comorbidity; quantification of FEPi in these patients provides additional clinical information in advanced VC detected by KI.

Aortic vascular calcification is inversely associated with the trabecular bone score in patients receiving dialysis

INTRODUCTION

Progressive chronic kidney disease (CKD) confers a marked increase in risk for vascular calcification, cardiovascular disease, fracture and mortality, with likely contributing factors including dysregulated bone metabolism and mineral homeostasis. In general population studies, increased vascular calcification is directly related to mortality and inversely related to bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA). In patients with CKD, abnormalities in turnover, mineralization and bone volume reduce the ability of DXA to predict fracture. The trabecular bone score (TBS) obtained from lumbar spine DXA images, provides a surrogate measure of microarchitectural integrity not captured by BMD. This study aimed to examine the association of the TBS to prevalent abdominal aortic calcification (AAC) in patients with CKD receiving dialysis.

METHODS

We performed a cross-sectional study of dialysis patients awaiting transplantation. All patients underwent laboratory testing, lateral spinal radiographs including the abdominal aorta, DXA imaging and TBS assessment. AAC scores were determined using the Kauppila method. Correlations and linear regression models were used to determine predictors of AAC scores.

RESULTS

146 patients (60% male, mean age 48 ± 13 years) were included, of whom 49% had prevalent calcification with an AAC score ≥ 1. Of those with calcification, the mean AAC score was 7 ± 5.5 and 42 patients had scores ≥ 6, considered to indicate severe AAC. TBS values corresponding to intermediate or high risk for fracture (<1.31) were present in 35% of patients. TBS values correlated inversely to AAC scores (β = -0.206, p = 0.013) and remained significant in multivariable linear regression, adjusting for age, BMI and time on dialysis (-0.160, p = 0.031). There was no significant correlation of AAC scores to any BMD parameter.

CONCLUSION

There is a high prevalence of AAC in relatively young dialysis patients awaiting transplantation and their AAC scores are inversely related to the TBS but not to DXA-derived BMD parameters. In patients with CKD on dialysis, TBS assessment reflects microarchitectural abnormalities of bone not captured by DXA. The inverse relationship of TBS to vascular calcification may provide insights into bone-vascular interactions in CKD.

Abdominal aortic calcification on dual-energy X-ray absorptiometry: Methods of assessment and clinical significance

Abdominal aortic calcification (AAC) can be accurately recognized on lateral spine images intended for vertebral fracture assessment, that are obtained with dual-energy X-ray absorptiometry (DXA). Greater amounts of AAC are common in the older population for whom DXA is routinely done, and have been consistently associated with incident atherosclerotic cardiovascular disease (ASCVD) events. AAC has also been associated with incident fractures in some prospective studies, but not in others. However, further research is needed to quantify the extent to which measurement of AAC improves prediction of ASCVD events and its impact on physician and patient ASCVD risk management. Additionally, research to develop better, more precise, automated, quantitative methods of AAC assessment on lateral spine densitometric images will hopefully lead to better prediction of clinical outcomes. In conclusion, although the prime indication for densitometric lateral spine imaging remains vertebral fracture assessment, AAC that is found incidentally on lateral spine images should be reported, so that patients and their health care providers are aware of its presence.

Opportunistic Use of CT Imaging for Osteoporosis Screening and Bone Density Assessment: A Qualitative Systematic Review

BACKGROUND

The purpose of this study was to determine the clinical opportunities for the use of computed tomography (CT) imaging for inferring bone quality and to critically analyze the correlation between dual x-ray absorptiometry (DXA) and diagnostic CT as reported in the literature.

METHODS

A systematic review of the MEDLINE database was performed in February 2016 using the PubMed interface. The inclusion criteria were English language, studies performed using living human subjects, studies pertaining to orthopaedics, use of conventional diagnostic CT scans, studies that measured cancellous bone, and studies that reported Hounsfield unit (HU) measurements directly rather than a computed bone mineral density.

RESULTS

Thirty-seven studies that reported on a total of 9,109 patients were included. Of these, 10 studies correlated HU measurements of trabecular bone with DXA-based bone assessment. Reported correlation coefficients ranged between 0.399 and 0.891, and 5 of the studies reported appropriate threshold HU levels for diagnosing osteoporosis or osteopenia.

CONCLUSIONS

Direct HU measurement from diagnostic CT scans has the potential to be used opportunistically for osteoporosis screening, but in its current state it is not ready for clinical implementation. There is a lack of exchangeability among different machines that limits its broad applicability. Future research efforts should focus on identifying thresholds at specific anatomic regions in high-risk patients in order to have the greatest impact on patients. However, using diagnostic CT to infer region-specific osteoporosis could be extraordinarily valuable to orthopaedic surgeons and primary care physicians, and merits further research.

Chronic Kidney Disease-Mineral and Bone Disorders (CKD-MBDs): What the Endocrinologist Needs to Know

OBJECTIVE

Chronic kidney disease-mineral and bone disorders (CKD-MBDs) are a spectrum of abnormalities involving skeletal hormones, minerals, and bone turnover and mineralization. This paper focuses on what the endocrinologist should know about the assessment and management of skeletal and metabolic disorders in CKD-MBDs.

METHODS

Relevant literature was reviewed to (1) define disturbances of minerals and hormones in the course of CKD; (2) identify the variable radiographic and histomorphometric changes of CKD-MBDs; (3) review the association among CKD-MBDs, vascular calcification, cardiovascular disease (CVD), and mortality; and (4) clarify issues in CKD-MBDs therapy.

RESULTS

Assessment and treatment of CKD-MBDs is complicated by progressive changes in bone minerals and skeletal regulatory hormones as kidney function declines. CKD-MBDs are associated with fracture risk, and studies demonstrate that bone mineral density can be used to assess bone loss and fracture risk in these patients. Treatment of CKD-MBDs continues to evolve. Use of calcium, phosphate binders, vitamin D, vitamin D-receptor analogs, and drugs for osteoporosis and CKD-MBDs treatment are discussed in the context of safety and efficacy for patients with CKD.

CONCLUSION

The association of CKD with bone disease, vascular calcification, CVD, and mortality mandates earlier recognition and treatment of CKD-MBDs. Osteoporosis as a distinct entity can be diagnosed and managed in CKD, although assessment of osteoporosis becomes challenging in late (stage 4 to 5) CKD. Diabetes is common in early (stage 1 to 3) CKD. In addition, 96% of all individuals identified as having CKD have early CKD. The endocrinologist is uniquely positioned to address and treat both diabetes and many of the metabolic and skeletal disorders associated with early CKD-MBDs, including osteoporosis.

Quantitative Assessment of Abdominal Aortic Calcifications Using Lateral Lumbar Radiograph, Dual-Energy X-ray Absorptiometry, and Quantitative Computed Tomography of the Spine

Abdominal aortic calcifications (AACs) represent an independent determinant of cardiovascular events and are strongly associated with cardiovascular disease. To our knowledge, a comparison between lateral lumbar radiography, lateral spine dual-energy x-ray absorptiometry (DXA), and quantitative computed tomography (QCT) in the assessment of AAC has not been performed. Our objective was to compare those methods in the detection and quantification of AAC using a simplified 8-point score system (AAC-8). Three hundred twenty-three postmenopausal women underwent lateral lumbar radiography, lateral spine DXA, and QCT for osteoporosis screening and were scored for AAC using the AAC-8. Lateral lumbar radiographs, lateral spine DXA, and QCT detected AAC in 58%, 55%, and 60% of the subjects, respectively. The nonparametric intraclass correlation coefficient between lateral lumbar radiograph and lateral spine DXA and lateral lumbar radiograph and QCT were 0.699 (95% confidence interval [CI]: 0.638-0.752) and 0.829 (95% CI: 0.783-0.865). Area under operating curve (receiver operating characteristic [ROC]) for lateral spine DXA was 0.826 (95% CI: 0.764-0.888), whereas for QCT was 0.948 (95% CI: 0.922-0.974) considering lateral lumbar radiograph as gold standard. AAC has been shown to be a significant predictive marker of overall cardiovascular disease. DXA may be a screening tool among asymptomatic patients with low radiation exposure to identify an important cardiovascular disease risk factor. QCT represents a reliable technique that may be applied as a future standard to facilitate the detection of abdominal aortic calcification as well as to provide more accurate measurement of bone densitometry.

Abdominal aortic calcification in patients with CKD

Background

Abdominal aortic calcification (AAC) is independently associated with cardiovascular events in dialysis patients and in the general population. However, data in non-dialysis chronic kidney disease (CKD) patients are limited. We analyzed determinants and prognostic value of AAC in non-dialysis CKD patients.

Methods

We included patients with CKD not receiving renal replacement therapy from the MASTERPLAN study, a randomized controlled trial that started in 2004. In the period 2008–2009, an X-ray to evaluate AAC was performed in a subgroup of patients. We studied AAC using a semi-quantitative scoring system by lateral lumbar X-ray. We used baseline and 2-year data to find determinants of AAC. We used a composite cardiovascular endpoint and propensity score matching to evaluate the prognostic value of AAC.

Results

In 280 patients an X-ray was performed. In 79 patients (28 %) the X-ray showed no calcification, in 62 patients (22 %) calcification was minor (<4), while 139 patients (50 %) had moderate or heavy calcification (≥4). Older age, prior cardiovascular disease, higher triglyceride levels, and higher phosphate levels were independent determinants of a calcification score ≥4. AAC score ≥4 was independently associated with cardiovascular events, with a hazard ratio of 5.5 (95 % confidence interval 1.2–24.8).

Conclusions

Assessment of AAC can identify CKD patients at higher cardiovascular risk, and may provide important information for personalized treatment. Whether this approach will ultimately translate into better outcomes remains to be answered.

Electronic supplementary material

The online version of this article (doi:10.1007/s40620-015-0260-7) contains supplementary material, which is available to authorized users.

Comparison of single CT scan assessment of bone mineral density, vascular calcification and fat mass with standard clinical measurements in renal transplant subjects: the ABC HeART study

Background

Despite limitations of routine methods, Clinical Practice Guidelines support the assessment of bone mineral density (BMD) and vascular calcification in renal transplant recipients. Changes in fat mass also occur post-transplantation, although they are traditionally difficult to measure accurately. We report the feasibility, convenience and accuracy of measuring the above 3 parameters using a novel CT protocol.

Methods

We conducted a cross-sectional study of 64 first renal allograft recipients (eGFR > 30 ml/min/1.73 m²). Quantitative CT (QCT) BMD analysis was conducted using CT lumbar spine (GE Medical Systems Lightspeed VCT & Mindways QCT Pro Bone Mineral Densitometry System Version 4.2.3) to calculate spinal volumetric BMD and compared with standard DXA calculated areal BMD at the spine, hip and distal forearm. Abdominal aortic calcification was assessed by semi-quantitative Aortic Calcification Index (ACI) method and compared with lateral lumbar x-ray Kappuila score and pulse wave velocity (PWV). Visceral and subcutaneous adipose tissue volume (Osirix 16 Ver 3.7.1) was compared with BMI.

Results

Participants were 61 % male, had a mean age of 47 years, median ESKD duration of 5.4 years and a mean eGFR of 54 ml/min. iDXA median T-score at proximal femur was −1.2 and at lumbar spine was −0.2. Median QCT Trabecular T-score at lumbar spine was −1.2. The percent of subjects with a T-score of <2.5 by site and method was DXA Proximal Femur: 7 %, DXA distal radius: 17 %, DXA spine: 9 %, QCT (American College of Radiology cutoffs): 9 %. CT derived ACI correlated with PWV (r = 0.29, p = 0.02), pulse wave pressure (r = 0.51, p < 0.001), QCT Trabecular (−0.31, p = 0.01) and cortical volumetric BMD and history of cardiovascular events (Mann–Whitney U, p = 0.02). Both visceral and subcutaneous adipose tissue correlated with BMI (r = 0.63 & 0.64, p < 0.001).

Conclusions

Single CT scan triple assessment of BMD, vascular calcification and body composition is an efficient, accurate and convenient method of risk factor monitoring post renal transplantation.

Abdominal aortic calcification detection using dual-energy X-ray absorptiometry: validation study in healthy women compared to computed tomography

Abdominal aortic calcification (AAC) is an independent determinant of cardiovascular events. Computed tomography (CT) is currently the gold standard measure of AAC but is limited by high radiation exposure. Lateral dual-energy X-ray absorptiometry (DXA) has the potential to detect AAC at a fraction of the radiation dose. Our objective was to determine the accuracy of lateral-DXA in detecting AAC compared to CT in healthy women. Women from the TwinsUK registry aged 52-80 years (n = 105) underwent noncontrast CT and lateral-DXA imaging of the abdominal aorta at lumbar vertebrae L1-L4. Presence of calcium on CT was scored using the volume method. Lateral-DXA images were scored using the previously validated semiquantitative 24-point score and simplified 8-point score. Calcification was present in 81 % of women as determined by CT and 49 % with lateral-DXA. The mean volume score and the 24- and 8-point scores of AAC were 0.20 ± 0.41 cm(2), 2.39 ± 3.91 arbitrary units, and 1.47 ± 2.13 arbitrary units, respectively. There was moderate agreement between CT and 24-point lateral-DXA (Spearman's rank correlation coefficient r = 0.58, P < 0.0001). The sensitivity of lateral-DXA for detecting AAC was 56 % and specificity was 80 %. Sensitivity and specificity of lateral-DXA improved to 64 and 84 % when analysis was limited to calcium volumes ≥0.008 cm(3) as detected by CT. Lateral-DXA imaging may provide a useful alternative to CT in detecting AAC with minimal radiation exposure, which may be used with concurrent bone mineral density assessment.

Dual-energy X-ray absorptiometry in the evaluation of abdominal aortic calcifications

The objective of this study was to evaluate the diagnostic performance of the new dual-energy X-ray absorptiometry equipment vs digital radiography (DR) in the detection and scoring of abdominal aortic calcifications (AACs). Seventy-five patients with indication for morphometric evaluation of the spine underwent vertebral fracture assessment (VFA) and spinal DR (gold standard). The radiographic and VFA images were analyzed to detect AAC using a previously validated 24-point scale (AAC-24) and a simplified 8-point scale (AAC-8). The evaluation was conducted by 2 expert radiologists and repeated by the more experienced of the 2 after 7d to verify the results. Patients with a score of 5 or more in AAC-24 and 3 or more in AAC-8 were considered at risk for cardiovascular diseases (CVDs). The aorta was not completely visible in 11 VFA and 1 DR images. DR detected AAC in 42 of the 63 patients (66.7%), whereas 15 patients (23.8%) were considered at risk for CVD. The VFA showed sensitivity, specificity, and accuracy in the detection of AAC with values of 78.6%, 85.7%, and 81.0%, respectively, with both AAC-24 and AAC-8; in the identification of patients at risk for CVD, VFA demonstrated sensitivity, specificity, and accuracy, respectively, with values of 86.7%, 100%, and 96.8% using AAC-24 and 86.7%, 93.8%, and 92.1% using AAC-8. In the detection of AAC, intraobserver agreement was superimposable using both the techniques (κ=1.00), whereas in the identification of patients at risk for CVD, kappa values were 0.96 and 0.95 using AAC-24 and 1.00 and 0.96 using AAC-8 for DR and VFA, respectively. Interobserver agreement in the evaluation of the presence/absence of AAC showed a kappa value of 0.76 for DR and 0.71 for VFA, whereas kappa values of 0.91 and 0.87 for DR and 0.85 and 0.83 for VFA were achieved for CVD risk using AAC-24 and AAC-8, respectively. AAC can be easily and accurately diagnosed by VFA with satisfactory accuracy, reproducibility, and repeatability. VFA may be used in the assessment and monitoring of AAC.