title: Repeat testing is essential when estimating chronic kidney disease prevalence and associated cardiovascular risk.
abstract: BACKGROUND
  Investigations into chronic kidney disease (CKD) and cardiovascular disease in the CKD population may be misleading as they are often based on a single test of kidney function.
  
  
  OBJECTIVE
  To determine whether repeat testing at 3 months to confirm a diagnosis of CKD impacts on the estimated prevalence of CKD and the estimated 10-year general cardiovascular risk of the CKD population.
  
  
  METHODS
  Blood and urine samples from presumed healthy volunteers were analysed for evidence of CKD on recruitment and again 3 months later. Estimated 10-year cardiovascular risk was calculated using criteria determined by the Framingham study. Preliminary study: 512 volunteers were screened for CKD. Of the initial results, 206 indicated CKD or eGFR within one standard deviation of abnormal, and 142 (69%) of these were retested. Validation study: 528 volunteers were recruited and invited to return for repeat testing. A total of 214 (40.5%) participants provided repeat samples.
  
  
  RESULTS
  A single test indicating CKD had a positive predictive value of 0.5 (preliminary) and 0.39 (validation) for repeat abnormalities 3 months later. Participants with CKD confirmed on repeat testing had a significant increase in estimated 10-year cardiovascular risk over the population as a whole (preliminary: 16.5 vs. 11.9%, P < 0.05; validation: 18.1 vs. 9.2%, P < 0.01). Participants with a solitary test indicating CKD had no elevation in cardiovascular risk.
  
  
  CONCLUSIONS
  Repeat testing for CKD after 3 months significantly reduces the estimated prevalence of disease and identifies a population with true CKD and a cardiovascular risk significantly in excess of the general population.
authors.affiliation: Oxford Kidney Unit, Oxford Radcliffe Hospitals NHS Trust, Churchill Hospital, Old Road, Headington, Oxford OX3 7LJ, UK. mattbrook1980@gmail.com
authors.forename: M O
authors.initials: MO
authors.lastname: Brook
authors.forename: M J
authors.initials: MJ
authors.lastname: Bottomley
authors.forename: C
authors.initials: C
authors.lastname: Mevada
authors.forename: A
authors.initials: A
authors.lastname: Svistunova
authors.forename: A-M
authors.initials: AM
authors.lastname: Bielinska
authors.forename: T
authors.initials: T
authors.lastname: James
authors.forename: A
authors.initials: A
authors.lastname: Kalachik
authors.forename: P N
authors.initials: PN
authors.lastname: Harden
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002318:Cardiovascular Diseases / Q000097:blood / Q000209:etiology* / Q000401:mortality / Q000652:urine; D003955:Diagnostic Tests, Routine / Q000592:standards*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D015995:Prevalence; D051436:Renal Insufficiency, Chronic / Q000097:blood / Q000150:complications* / Q000175:diagnosis* / Q000652:urine; D012307:Risk Factors; D055815:Young Adult