title: Variability in monthly serum bicarbonate measures in hemodialysis patients: a cohort study.
abstract: BACKGROUND
  Some nephrologists have advocated an individualized approach to the prescription of bicarbonate hemodialysis. However, the utility of monthly serum bicarbonate levels for guiding and evaluating such treatment decisions has not been evaluated. We sought to define the variability of these measurements and to determine factors that are associated with month-to-month variability in pre-dialysis serum bicarbonate.
  
  
  METHODS
  We examined the monthly variability in serum bicarbonate measurements among 181 hemodialysis patients admitted to a free-standing dialysis unit in the Bronx, NY from 1/1/2008-6/30/2012. All patients were treated with a uniform bicarbonate dialysis prescription (bicarbonate 35 mEq/L, acetate 8 mEq/L). Pre-dialysis serum bicarbonate values were obtained from monthly laboratory reports. Month-to-month variability was defined using a rolling measurement for each time point.
  
  
  RESULTS
  Only 34 % of high serum bicarbonate values (>26 mEq/L) remained high in the subsequent month, whereas 60 % converted to normal (22-26 mEq/L). Of all low values (<22 mEq/L), 41 % were normal the following month, while 58 % remained low. Using the mean 3-month bicarbonate, only 29 % of high values remained high in the next 3-month period. In multivariable-adjusted longitudinal models, both low and high serum bicarbonate values were associated with greater variability than were normal values (β = 0.12 (95 % CI 0.09-0.15) and 0.24 (0.18 to 0.29) respectively). Variability decreased with time, and was significantly associated with age, phosphate binder use, serum creatinine, potassium, and normalized protein catabolic rate.
  
  
  CONCLUSIONS
  Monthly pre-dialysis serum bicarbonate levels are highly variable. Even if a clinician takes no action, approximately 50 % of bicarbonate values outside a normal range of 22-26 mEq/L will return to normal in the subsequent month. The decision to change the bicarbonate dialysis prescription should not be based on a single bicarbonate value, and even a 3-month mean may be insufficient.
authors.affiliation: Department of Medicine, Thomas Jefferson University School of Medicine, Philadelphia, PA, USA. ravi.patel@med.einstein.yu.edu.
authors.forename: Ravi
authors.initials: R
authors.lastname: Patel
authors.affiliation: Division of Nephrology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY, USA. bill.paredes@einstein.yu.edu.
authors.forename: William
authors.initials: W
authors.lastname: Paredes
authors.affiliation: Department of Epidemiology & Population Health, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Ullmann 615, Bronx, NY, 10461, USA. charles.hall@einstein.yu.edu.|The Saul R. Korey Department of Neurology, Albert Einstein College of Medicine, Bronx, NY, USA. charles.hall@einstein.yu.edu.
authors.forename: Charles B
authors.initials: CB
authors.lastname: Hall
authors.affiliation: Division of Nephrology, Department of Medicine, Medstar Georgetown University, Washington, DC, USA. mknader@hotmail.com.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Nader
authors.affiliation: Department of Medicine, Interfaith Medical Center, Brooklyn, NY, USA. deepaksapkota49@gmail.com.
authors.forename: Deepak
authors.initials: D
authors.lastname: Sapkota
authors.affiliation: Division of Nephrology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY, USA. vaughnfolkert1@mac.com.
authors.forename: Vaughn W
authors.initials: VW
authors.lastname: Folkert
authors.affiliation: Division of Nephrology, Department of Medicine, Albert Einstein College of Medicine, Bronx, NY, USA. matthew.abramowitz@einstein.yu.edu.|Department of Epidemiology & Population Health, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Ullmann 615, Bronx, NY, 10461, USA. matthew.abramowitz@einstein.yu.edu.
authors.forename: Matthew K
authors.initials: MK
authors.lastname: Abramowitz
mesh_terms: D001639:Bicarbonates / Q000097:blood*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D006435:Renal Dialysis; D012189:Retrospective Studies; D013997:Time Factors
chemical_list: D001639:Bicarbonates