title: Capillary rarefaction in advanced chronic kidney disease is associated with high phosphorus and bicarbonate levels.
abstract: BACKGROUND
  In patients with chronic kidney disease (CKD), disorders of mineral metabolism are associated with vascular calcifications and mortality. Microvascular dysfunction, by affecting flow resistance and tissue perfusion, may explain the cardiovascular sequelae of CKD-associated disorders of mineral metabolism. We investigated whether advanced CKD is associated with a decrease in the functional and structural number of capillaries in skin and subsequently whether capillary rarefaction is related to mineral metabolism.
  
  
  METHODS
  Capillary density was measured by nailfold microscopy in 19 predialysis and 35 CKD Stage 5 (CKD5) patients and 19 controls. In CKD patients, calcium, phosphorus, parathyroid hormone, 25-hydroxyvitaminD3 (25vitD3) and 1,25-dihydroxyvitaminD3 (1,25vitD3) were analysed as well.
  
  
  RESULTS
  Capillary density at baseline was 42 ± 15/mm(2) in predialysis patients, 45 ± 17/mm(2) in CKD5 patients and 56 ± 20/mm(2) in controls (patients versus controls, respectively, P < 0.05 and P = 0.05). Absolute capillary recruitment during post-occlusive reactive hyperaemia was 17 ± 7/mm(2), 14 ± 6/mm(2) and 23 ± 8/mm(2), respectively (P < 0.05 for both patients and controls). Capillary density during venous occlusion was 59 ± 20/mm(2), 59 ± 21/mm(2) and 77 ± 21/mm(2), respectively (P < 0.05 for both patients and controls). In multiple regression analysis, both serum phosphorus and bicarbonate values were independently and inversely associated with capillary density at baseline (r(2) of model = 19%) as well as during venous occlusion (r(2) of model = 28%). Furthermore, both serum phosphorus and bicarbonate were inversely and female gender positively correlated with capillary density during recruitment (r(2) of model = 37%).
  
  
  CONCLUSIONS
  Advanced CKD is characterized by an impaired functional and structural capillary density in skin, which is related to both high phosphorus and bicarbonate values.
authors.affiliation: Department of Nephrology, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Oanh H D
authors.initials: OH
authors.lastname: Thang
authors.forename: Erik H
authors.initials: EH
authors.lastname: Serné
authors.forename: Muriel P C
authors.initials: MP
authors.lastname: Grooteman
authors.forename: Yvo M
authors.initials: YM
authors.lastname: Smulders
authors.forename: Piet M
authors.initials: PM
authors.lastname: ter Wee
authors.forename: Geert-Jan
authors.initials: GJ
authors.lastname: Tangelder
authors.forename: Menso J
authors.initials: MJ
authors.lastname: Nubé
mesh_terms: D001639:Bicarbonates / Q000097:blood*; D002112:Calcifediol / Q000097:blood; D002117:Calcitriol / Q000097:blood; D002196:Capillaries / Q000002:abnormalities* / Q000503:physiopathology*; D016022:Case-Control Studies; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000097:blood; D005500:Follow-Up Studies; D006801:Humans; D007676:Kidney Failure, Chronic / Q000150:complications*; D008297:Male; D008875:Middle Aged; D010758:Phosphorus / Q000097:blood*; D011379:Prognosis; D012867:Skin / Q000098:blood supply*; D014652:Vascular Diseases / Q000209:etiology* / Q000378:metabolism
chemical_list: D001639:Bicarbonates; D010758:Phosphorus; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D002117:Calcitriol; D002112:Calcifediol