title: Chronic Kidney Disease in Cats and the Risk of Total Hypercalcemia.
abstract: BACKGROUND
  Chronic kidney disease (CKD) is a common comorbidity in cats with hypercalcemia, but whether CKD is a risk factor for hypercalcemia is unclear. Hypercalcemia often is diagnosed based on total calcium concentration (tCa), which tends to underestimate the ionized calcium concentration (iCa) in cats.
  
  
  OBJECTIVE
  Assessment of the performance of tCa for the diagnosis of ionized hypercalcemia, and exploration of factors influencing the relationship between iCa and tCa. Determination of risk factors for incident total hypercalcemia (ie, the development of hypercalcemia based on tCa during follow-up).
  
  
  METHODS
  Records of a cross-section (n = 477) and observational cohort (n = 367) of client-owned cats with and without azotemic CKD from first opinion practice.
  
  
  METHODS
  Retrospective cross-sectional and retrospective cohort study. The diagnostic accuracy of tCa as an index test for ionized hypercalcemia was evaluated, and risk factors for underestimation were explored by binary logistic and linear regression in a cross-section of cats with and without azotemic CKD. Chronic kidney disease and clinicopathological variables were assessed as predictors of incident total hypercalcemia by both time-invariant and time-dependent Cox regression in a cohort of cats.
  
  
  RESULTS
  Specificity of tCa for identification of ionized hypercalcemia was high (100%), but sensitivity was low. Underestimation was associated with lower venous bicarbonate concentrations. Cats with CKD had increased risk for incident total hypercalcemia (hazard ratio, 4.29; 95% confidence interval, 1.96-9.37; P < .001). Higher tCa predicted incident total hypercalcemia in both azotemic and nonazotemic cats (P < .001).
  
  
  CONCLUSIONS
  Chronic kidney disease is a risk factor for incident total hypercalcemia, and most cats with increased tCa had concurrent ionized hypercalcemia. Higher baseline tCa predicts incident total hypercalcemia. Prospective studies assessing changes in iCa are warranted.
authors.affiliation: Department of Comparative Biomedical Sciences, Royal Veterinary College, University of London, London, UK.
authors.forename: D H N
authors.initials: DH
authors.lastname: van den Broek
authors.affiliation: Research Support Office, Royal Veterinary College, University of London, London, UK.
authors.forename: Y-M
authors.initials: YM
authors.lastname: Chang
authors.affiliation: Department of Comparative Biomedical Sciences, Royal Veterinary College, University of London, London, UK.
authors.forename: J
authors.initials: J
authors.lastname: Elliott
authors.affiliation: Department of Clinical Science and Services, Royal Veterinary College, University of London, North Mymms, Hatfield, Hertfordshire, UK.
authors.forename: R E
authors.initials: RE
authors.lastname: Jepson
mesh_terms: D000818:Animals; D002118:Calcium / Q000097:blood; D002371:Cat Diseases / Q000175:diagnosis*; D002415:Cats; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D006934:Hypercalcemia / Q000150:complications / Q000662:veterinary*; D008297:Male; D051436:Renal Insufficiency, Chronic / Q000150:complications / Q000662:veterinary*; D012189:Retrospective Studies; D012680:Sensitivity and Specificity
chemical_list: D002118:Calcium
keywords: Azotemia; Bicarbonate; Calcium; Feline