title: Limiting the testing of urea: Urea along with every plasma creatinine test?
abstract: BACKGROUND
  We found that it is not necessary to simultaneously detect both creatinine (CREA) and urea until the concentration of CREA is lower than the certain level. To reduce urea testing, we suggest measuring urea only when CREA or estimated glomerular filtration rate (eGFR) exceeds a predetermined limit.
  
  
  METHODS
  CREA and urea data were analyzed consisting of almost all of people age above 65 years old check-up (n=95441) in Shuyang countryside, and inpatients (n=101631), outpatients (n=18474) and Routine Health Check-up (n=20509) in Shuyang People's Hospital. The proportions of elevated urea were derived. The data used in this study was generated from people more than 13 years old in both outpatients and inpatients.
  
  
  RESULTS
  When the limits for initiating urea testing were used at 85 μmol/L CREA and 120 mL/min/1.73 m2eGFR, the percentage of unnecessary urea test are 94.5% and 64.7% (elderly health check-up), 67.9% and 84.5% (outpatients), 88.5% and 73.2% (inpatients), 92.2% and 81.7% (routine health check-up). The missing rate of urea are 1%, 2.5%, 4.6% and 9.2%, 0.1%, 0.4%, 0.9% and 1.8%, 0.4%, 0.8%, 1.4%, and 2.5%, 0.05%, 0.1%, 1.1%, and 0.8% of ureas exceeding 9.28 mmol/L and 8.3 mmol/L in above each group, respectively. If the CREA≤85 μmol/L or eGFR≥90 mL/min/1.73 m2, there is 97.5% urea <10.1 mmol/L, the proportion of elevated urea missed is 2.5%.
  
  
  CONCLUSIONS
  We suggest that the initiating urea testing should be based on the upper limit of Reference Intervals serum CREA of females or a 120 mL/min/1.73 m2eGFR limit. Conservatively, the urea testing would be reduced by 65% at least.
authors.affiliation: Shuyang People's Hospital, Shuyang, China.
authors.forename: Gao-Ming
authors.initials: GM
authors.lastname: Zhang
authors.affiliation: Affiliated Hospital of Shandong University of Traditional Chinese Medicine, Jinan, China.
authors.forename: Xu-Xiao
authors.initials: XX
authors.lastname: Guo
authors.affiliation: Shuyang People's Hospital, Shuyang, China.
authors.forename: Guo-Ming
authors.identifier: http://orcid.org/0000-0003-0662-1302
authors.initials: GM
authors.lastname: Zhang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001774:Blood Chemical Analysis / Q000592:standards* / Q000706:statistics & numerical data*; D003404:Creatinine / Q000097:blood*; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D008297:Male; D000069342:Medical Overuse / Q000517:prevention & control; D008875:Middle Aged; D012016:Reference Values; D014508:Urea / Q000097:blood*; D055815:Young Adult
chemical_list: D014508:Urea; D003404:Creatinine
keywords: creatinine; estimated glomerular filtration rate; kidney function tests; urea