Capillary rarefaction: an early marker of microvascular disease in young hemodialysis patients

BACKGROUND: Pediatric patients with chronic kidney disease (CKD) are at increased risk of early cardiovascular disease and premature death. Abnormalities in microvascular structure and function may presage end-organ damage including vascular calcification and myocardial ischemia associated with disordered mineral metabolism. Early detection of microvascular rarefaction (reduced density of capillaries) may identify at-risk patients and prompt timely therapeutic interventions. Our objective was to study capillary rarefaction in pediatric hemodialysis (HD) patients and to determine possible associations with mineral metabolism and cardiac risk biomarkers. METHODS: Capillary density (CD) was measured by nailfold capillaroscopy in 19 pediatric HD patients and 20 healthy controls. Demographic and biochemical markers were collected at entry and 6-month follow-up. RESULTS: CD was significantly decreased in HD patients compared with controls with a deficit of 24 and 31% at baseline and subsequent follow-up. Maximal CD correlated significantly with intact parathyroid hormone (iPTH) (r = −0.45; P = 0.005), serum calcium (r = −0.38; P = 0.02) and 25(OH) vitamin D levels (r = +0.36; P = 0.03) in HD patients. Capillary functional measures were similar to controls. By multivariate analysis, the primary negative determinants of CD were African American race and hyperparathyroidism; whereas, glomerular disease had a positive influence on capillary rarefaction (R(2) = 64.2% variance; P = 0.001). CONCLUSION: Pediatric HD patients demonstrate a ‘structural deficit’ in CD but show preserved ‘functional integrity’. Capillary rarefaction, an early risk factor of incipient vascular calcification, was strongly associated with biomarkers of altered mineral metabolism. Further studies are warranted to determine the impact of optimizing blood pressure and metabolic control on changes in capillary rarefaction in young CKD patients.