title: Serum samples that have been stored long-term (>10 years) can be used as a suitable data source for developing cardiovascular risk prediction models in large observational rheumatoid arthritis cohorts.
abstract: OBJECTIVE
  There is an unmet need for a specific cardiovascular risk (CV) algorithm for rheumatoid arthritis (RA) patients. Lipoprotein data are often not available in RA cohorts but could be obtained from frozen blood samples. The objective of this study was to estimate the storage effect on lipoproteins in long-term (>10 years) frozen serum samples.
  
  
  METHODS
  Data were used from an inception RA cohort. Multiple serum samples from 152 patients were analyzed for lipoproteins, being frozen for 1-26 years at -20°C. Storage effect on lipoproteins was estimated using longitudinal regression analyses and a lipid decay correction factor was developed. Clinical impact of the storage effect on lipoproteins was assessed by calculating the number of patients reclassified to another CV risk group according to the SCORE risk calculator after applying the decay correction factor.
  
  
  RESULTS
  There was a significant effect of storage time on total cholesterol (TC) (P<0.001) and high density lipoprotein cholesterol (HDL-c) levels (P<0.001), not LDL-c (P=0.83). The lipid decay correction factor was 0.03 mmol/L and 0.024 mmol/L per additional year of storage for TC and HDL-c, respectively. The TC:HDL ratio decreased after correction for storage effect. After correction, only 5% of patients were reclassified to another CV risk group.
  
  
  CONCLUSIONS
  A modest storage decay effect on lipoproteins was found that is unlikely to significantly affect CV risk stratification. Serum samples that have been stored long-term (>10 years) can be used to obtain valid lipid levels for developing CV risk prediction models in RA cohorts, even without applying a decay correction factor.
authors.affiliation: Department of Rheumatology, Radboud University Medical Centre, Nijmegen, The Netherlands.
authors.forename: Elke E A
authors.initials: EE
authors.lastname: Arts
authors.affiliation: Department of Rheumatology, Radboud University Medical Centre, Nijmegen, The Netherlands.
authors.forename: Calin D
authors.initials: CD
authors.lastname: Popa
authors.affiliation: Department of Rheumatology, Dudley Group NHS Foundation Trust, Dudley, UK.
authors.forename: Jacqueline P
authors.initials: JP
authors.lastname: Smith
authors.affiliation: Department of Rheumatology, Radboud University Medical Centre, Nijmegen, The Netherlands.
authors.forename: Onno J
authors.initials: OJ
authors.lastname: Arntz
authors.affiliation: Department of Rheumatology, Radboud University Medical Centre, Nijmegen, The Netherlands.
authors.forename: Fons A
authors.initials: FA
authors.lastname: van de Loo
authors.affiliation: Department of Epidemiology, Biostatistics and Health Technology Assessment, Radboud University Medical Centre, Nijmegen, The Netherlands.
authors.forename: Rogier
authors.initials: R
authors.lastname: Donders
authors.affiliation: Department of Rheumatology, Diakonhjemmet Hospital, Oslo, Norway.
authors.forename: Anne Grete P
authors.initials: AG
authors.lastname: Semb
authors.affiliation: Department of Rheumatology, Dudley Group NHS Foundation Trust, Dudley, UK.
authors.forename: George D
authors.initials: GD
authors.lastname: Kitas
authors.affiliation: Department of Rheumatology, Radboud University Medical Centre, Nijmegen, The Netherlands.
authors.forename: Piet L C M
authors.initials: PL
authors.lastname: van Riel
authors.affiliation: Department of Rheumatology, Radboud University Medical Centre, Nijmegen, The Netherlands.
authors.forename: Jaap
authors.initials: J
authors.lastname: Fransen
mesh_terms: D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000473:pathology; D001800:Blood Specimen Collection; D002318:Cardiovascular Diseases / Q000097:blood* / Q000150:complications / Q000473:pathology; D002784:Cholesterol / Q000097:blood; D008076:Cholesterol, HDL / Q000097:blood; D005260:Female; D006801:Humans; D008055:Lipids / Q000097:blood; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D018570:Risk Assessment; D014280:Triglycerides / Q000097:blood
chemical_list: D008076:Cholesterol, HDL; D008055:Lipids; D014280:Triglycerides; D002784:Cholesterol