Schein 2000.

Methods	Study design: randomized clinical trial Number of study centers: 9 Number randomized: 19,557 operations (18,189 participants) (sample size calculations based on risk of adverse events) Study follow‐up: 1 week postsurgery
Participants	Country: USA and Canada Age (per operation): routine‐testing group = 73 ± 8 years; no‐testing group = 74 ± 8 years Gender (per operation): 7631 men; 11,926 women (routine‐testing group: men = 3769, women = 6006; no‐testing group: men = 3862, women = 5920) Inclusion criteria: people scheduled to undergo cataract surgery Exclusion criteria: less than 50 years old; were receiving general anesthesia; had a myocardial infarction within the preceding 3 months; had any preoperative medical testing done during the 28 days prior to enrollment; could not speak English or Spanish; 2nd eye not eligible if surgery was within 28 days of surgery in 1st randomized eye
Interventions	Intervention: routine testing with electrocardiography, complete blood count, and measurement of serum levels of electrolytes, urea nitrogen, creatinine, and glucose (operations scheduled: operations: n = 9775, participants: n = 9456; operations performed: operations: n = 9624, participants: n = 9411) Comparison: no preoperative testing unless the participant presented with a new or worsening condition that would warrant medical testing even if no surgery was scheduled (operations scheduled: operations: n = 9782, participants: n = 9445; operations performed: operations: n = 9626, participants: n = 9408)
Outcomes	Primary outcome: adverse medical events and interventions on the day of surgery and up to 7 days after surgery Secondary outcome: whether preoperative testing could have prevented the adverse event from occurring
Notes	Study date: 1 June 1995 to 30 June 1997 Publication language: English Participation rate: 94% Funding source: Agency for Health Care Policy and Research
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomization was stratified according to clinical center, age (in decades), and health status reported by participants using blocks of 4.
Allocation concealment (selection bias)	Low risk	Randomization was done by computer at time of enrollment.
Masking (performance bias) Were the participants masked to the treatment group?	High risk	Participants were informed of group assignment and given a letter and study brochure to present to the healthcare provider performing the preoperative assessment.
Masking (performance bias) Were the physicians performing the preoperative tests masked to the treatment group?	High risk	Healthcare providers performing the preoperative tests received a letter and study brochure from the participant at the time of the preoperative assessment.
Masking (detection bias) Were the primary outcome assessors masked to the treatment group?	Low risk	Medical events and treatments were recorded by an anesthesiologist or nurse anesthetist using a standardized form during surgery, and by a standardized telephone interview conducted by a study co‐ordinator 1 week following surgery. Additional patient information was recorded by nursing staff before discharge. 2 investigators reviewed medical charts to verify adverse events, and a 3rd investigator who was masked to the treatment assignment made the final clinical judgement.
Masking (detection bias) Were the secondary outcome assessors masked to the treatment group?	Low risk	2 investigators reviewed medical charts to verify adverse events, and a 3rd investigator who was masked to the treatment assignment made the final clinical judgement.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Intention‐to‐treat analysis was used. Data were 100% from day of surgery and 99.8% for 1 week after surgery.
Selective reporting (reporting bias)	Low risk	Reported the results for adverse medical events defined in methods section using a standardized form and standardized telephone interview