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

Vascular calcification (VC) is a major contributor to increased cardiovascular (CV) disease in chronic kidney disease (CKD) and an independent predictor of mortality. VC is inversely correlated with bone mineral density (BMD). Screening for VC may be useful to determine those at greater CV risk and dual-energy X-ray absorptiometry (DXA) may have a dual role in providing VC measurement as well as BMD.

We report cross-sectional data on 44 patients with CKD stages 3-4 and aim to determine and validate measurement of VC using DXA. Patients had computed tomography (CT) of abdominal aorta and DXA of lateral lumbar spine, to determine both aortic VC and BMD. Semi-quantitative measurement of VC from DXA was determined (blinded) using previously validated 8- and 24-point scales, and compared with VC from CT. BMD determination from L2 to L4 vertebrae on CT was compared with DXA-reported BMD.

Patients 66% male, 57% diabetic, had mean age 63.4 years and mean estimated glomerular filtration rate 31.4 +/- 12 mL/min. Aortic VC was present in 95% on CT, mean 564.9 +/- 304 Hounsfield units (HU). Aortic VC was seen in 68% on lateral DXA, mean scores 5.1 +/- 5.9 and 1.9 +/- 1.9 using 24- and 8-point scales, respectively. Strong correlation of VC measurement was present between CT and DXA (r 0.52, P < 0.001). For DXA VC 24-point score, intraclass correlations for intra-rater and inter-rater agreement were 0.91 and 0.64, respectively (8-point scale, intraclass correlations 0.90 and 0.69). Vertebral BMD measured by CT (mean 469.3 HU L2-4) also significantly correlated with lateral DXA-reported BMD (mean spine T-score -0.67 +/- 1.6) (r 0.56, P < 0.001).

Despite limitations in CKD, DXA may be useful as lateral DXA images provide concurrent assessment of aortic calcification as well as lumbar spine BMD, both correlating significantly with CT measurements. Lateral DXA may provide VC screening to determine patients at greater CV risk although more studies are needed to evaluate their potential role.