title: Socio-economic status influences chronic kidney disease prevalence in primary care: a community-based cross-sectional analysis.
abstract: BACKGROUND
  Primary care chronic kidney disease (CKD) registers report widely varying prevalence within the UK. We examined the effects of laboratory ascertainment and adjusting for practice-level variables on the variation in CKD prevalence. We carried out an Ayrshire-wide laboratory database analysis of primary care practices (PCPs).
  
  
  METHODS
  We analysed 54 PCPs with 313 639 registered patients aged ≥ 18. All patients with a low estimated glomerular filtration rate (<60 mL/min/1.73 m(2)) had their serum creatinine values extracted from 1st January 2009 to 31st March 2012. Individuals with CKD stage 3-5 were identified with an algorithm that confirmed chronicity. These data were linked to PCP attributes from Information Services Division, Scotland. Using laboratory-ascertained CKD prevalence, we examined whether adjusting for practice-level factors [socio-economic status (SES), rurality and patients to general practitioner ratio (PGR)] and patient-level factors (age, gender) explained some of the observed variation among PCPs. Individual and combined hierarchical multilinear regression models were used.
  
  
  RESULTS
  Eighteen thousand two hundred and eighty-five (5.8%) had CKD stage 3-5 on 31 March 2011. SES, rurality and PGR predicted 39% (F(3,50) = 12.37, P < 0.001) of the variation in prevalence with SES exerting the most influence (25%). With the stepwise addition of explanatory variables, variation between practices fell from 3.9-fold using PCP register prevalence to laboratory ascertained (3.1-fold variation), with age and gender adjustment (further fall to 2.1-fold), and lastly to 1.8-fold variation with adjustment for SES. Funnel plots using these adjustments reduced the number of outliers outside of 3 SD from 15 to 7 to 6, and outliers between 2 and 3 SD by 16 to 13 to 5.
  
  
  CONCLUSIONS
  Laboratory ascertainment is practicable, reduces variation and facilitates benchmarking. PCP attributes other than age and gender impact on prevalence. Over a third of variation in CKD prevalence among PCPs can be explained by rurality, PGR and especially SES even after age and gender stratification.
authors.affiliation: John Stevenson Lynch Renal Unit, University Hospital Crosshouse, NHS Ayrshire & Arran, Kilmarnock KA2 0BE, UK Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK.
authors.forename: Beng H
authors.initials: BH
authors.lastname: So
authors.affiliation: School of Clinical Sciences, University of Bristol, Bristol, UK.
authors.forename: Shona
authors.initials: S
authors.lastname: Methven
authors.affiliation: John Stevenson Lynch Renal Unit, University Hospital Crosshouse, NHS Ayrshire & Arran, Kilmarnock KA2 0BE, UK.
authors.forename: Mario D
authors.initials: MD
authors.lastname: Hair
authors.affiliation: Institute of Cardiovascular and Medical Sciences, University of Glasgow, Glasgow, UK.
authors.forename: Alan G
authors.initials: AG
authors.lastname: Jardine
authors.affiliation: John Stevenson Lynch Renal Unit, University Hospital Crosshouse, NHS Ayrshire & Arran, Kilmarnock KA2 0BE, UK.
authors.forename: Mark S
authors.initials: MS
authors.lastname: MacGregor
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D055812:Community-Based Participatory Research; D003430:Cross-Sectional Studies; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007677:Kidney Function Tests; D008297:Male; D008875:Middle Aged; D010818:Practice Patterns, Physicians'; D015995:Prevalence; D011320:Primary Health Care; D051436:Renal Insufficiency, Chronic / Q000175:diagnosis / Q000453:epidemiology*; D018570:Risk Assessment; D012606:Scotland / Q000453:epidemiology; D012923:Social Class; D055815:Young Adult
keywords: Scottish index of multiple deprivation; chronic kidney disease; laboratory ascertainment; rurality; variation