title: Seasonal variations in mortality, clinical, and laboratory parameters in hemodialysis patients: a 5-year cohort study.
abstract: OBJECTIVE
  Mortality varies seasonally in the general population, but it is unknown whether this phenomenon is also present in hemodialysis patients with known higher background mortality and emphasis on cardiovascular causes of death. This study aimed to assess seasonal variations in mortality, in relation to clinical and laboratory variables in a large cohort of chronic hemodialysis patients over a 5-year period.
  
  
  METHODS
  This study included 15,056 patients of 51 Renal Research Institute clinics from six states of varying climates in the United States. Seasonal differences were assessed by chi-squared tests and univariate and multivariate cosinor analyses.
  
  
  RESULTS
  Mortality, both all-cause and cardiovascular, was significantly higher during winter compared with other seasons (14.2 deaths per 100 patient-years in winter, 13.1 in spring, 12.3 in autumn, and 11.9 in summer). The increase in mortality in winter was more pronounced in younger patients, as well as in whites and in men. Seasonal variations were similar across climatologically different regions. Seasonal variations were also observed in neutrophil/lymphocyte ratio and serum calcium, potassium, and platelet values. Differences in mortality disappeared when adjusted for seasonally variable clinical parameters.
  
  
  CONCLUSIONS
  In a large cohort of dialysis patients, significant seasonal variations in overall and cardiovascular mortality were observed, which were consistent over different climatic regions. Other physiologic and laboratory parameters were also seasonally different. Results showed that mortality differences were related to seasonality of physiologic and laboratory parameters. Seasonal variations should be taken into account when designing and interpreting longitudinal studies in dialysis patients.
authors.affiliation: Renal Research Institute, 207 East 94 Street, Suite 303, New York, NY 10128, USA. lusvyat@rriny.com
authors.forename: Len A
authors.initials: LA
authors.lastname: Usvyat
authors.forename: Mary
authors.initials: M
authors.lastname: Carter
authors.forename: Stephan
authors.initials: S
authors.lastname: Thijssen
authors.forename: Jeroen P
authors.initials: JP
authors.lastname: Kooman
authors.forename: Frank M
authors.initials: FM
authors.lastname: van der Sande
authors.forename: Paul
authors.initials: P
authors.lastname: Zabetakis
authors.forename: Paul
authors.initials: P
authors.lastname: Balter
authors.forename: Nathan W
authors.initials: NW
authors.lastname: Levin
authors.forename: Peter
authors.initials: P
authors.lastname: Kotanko
mesh_terms: D000328:Adult; D000368:Aged; D001794:Blood Pressure; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D006435:Renal Dialysis / Q000401:mortality*; D012189:Retrospective Studies; D012621:Seasons; D015430:Weight Gain
references.citation: Am J Kidney Dis. 2000 May;35(5):812-8
references.pmid: 10793013
references.citation: Environ Res. 2003 May;92(1):8-13
references.pmid: 12706750
references.citation: Am J Kidney Dis. 2000 Sep;36(3):562-5
references.pmid: 10977788
references.citation: Kidney Int. 2007 Oct;72(8):1004-13
references.pmid: 17687259
references.citation: South Med J. 2004 Nov;97(11):1093-9
references.pmid: 15586600
references.citation: Kidney Int. 2004 May;65(5):1795-801
references.pmid: 15086919
references.citation: Nephron. 2001 Mar;87(3):199-214
references.pmid: 11287755
references.citation: Am J Cardiol. 1997 May 1;79(9):1194-7
references.pmid: 9164884
references.citation: Chronobiol Int. 1991;8(2):149-59
references.pmid: 1797411
references.citation: J Pharmacol Exp Ther. 2007 Jan;320(1):180-93
references.pmid: 17050784
references.citation: Blood Purif. 2008;26(2):196-203
references.pmid: 18319588
references.citation: Nephrol Dial Transplant. 2003 Jun;18(6):1167-73
references.pmid: 12748351
references.citation: QJM. 2003 Jan;96(1):45-52
references.pmid: 12509648
references.citation: Blood Purif. 2006;24(5-6):499-507
references.pmid: 17019079
references.citation: Lancet. 1997 May 10;349(9062):1341-6
references.pmid: 9149695
references.citation: J Am Soc Nephrol. 2002 Sep;13(9):2345-52
references.pmid: 12191979
references.citation: Public Health Nutr. 2000 Mar;3(1):19-29
references.pmid: 10786720
references.citation: Lancet. 1987 Jan 24;1(8526):212
references.pmid: 2880030
references.citation: N Engl J Med. 1998 Nov 5;339(19):1364-70
references.pmid: 9801397
references.citation: Am J Cardiol. 2007 Oct 1;100(7):1134-8
references.pmid: 17884377
references.citation: Blood Purif. 2002;20(4):370-5
references.pmid: 12169847
references.citation: Eur J Appl Physiol. 2009 Oct;107(3):251-71
references.pmid: 19609553
references.citation: Biol Res Nurs. 2007 Jul;9(1):30-41
references.pmid: 17601855