title: Preoperative screening: value of previous tests.
abstract: OBJECTIVE
  To determine the frequency of tests done in the year before elective surgery that might substitute for preoperative screening tests and to determine the frequency of test results that change from a normal value to a value likely to alter perioperative management.
  
  
  METHODS
  Retrospective cohort analysis of computerized laboratory data (complete blood count, sodium, potassium, and creatinine levels, prothrombin time, and partial thromboplastin time).
  
  
  METHODS
  Urban tertiary care Veterans Affairs Hospital.
  
  
  METHODS
  Consecutive sample of 1109 patients who had elective surgery in 1988.
  
  
  RESULTS
  At admission, 7549 preoperative tests were done, 47% of which duplicated tests performed in the previous year. Of 3096 previous results that were normal as defined by hospital reference range and done closest to the time of but before admission (median interval, 2 months), 13 (0.4%; 95% CI, 0.2% to 0.7%), repeat values were outside a range considered acceptable for surgery. Most of the abnormalities were predictable from the patient's history, and most were not noted in the medical record. Of 461 previous tests that were abnormal, 78 (17%; CI, 13% to 20%) repeat values at admission were outside a range considered acceptable for surgery (P less than 0.001, frequency of clinically important abnormalities of patients with normal previous results with those with abnormal previous results).
  
  
  CONCLUSIONS
  Physicians evaluating patients preoperatively could safely substitute the previous test results analyzed in this study for preoperative screening tests if the previous tests are normal and no obvious indication for retesting is present.
authors.affiliation: University of Minnesota, Minneapolis.
authors.forename: D S
authors.initials: DS
authors.lastname: Macpherson
authors.forename: R
authors.initials: R
authors.lastname: Snow
authors.forename: R P
authors.initials: RP
authors.lastname: Lofgren
mesh_terms: D000368:Aged; D015331:Cohort Studies; D016001:Confidence Intervals; D003955:Diagnostic Tests, Routine / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D008297:Male; D008403:Mass Screening / Q000706:statistics & numerical data; D008875:Middle Aged; D011237:Predictive Value of Tests; D011300:Preoperative Care / Q000379:methods*; D012016:Reference Values; D012189:Retrospective Studies; D013997:Time Factors