Are routine preoperative laboratory screening tests necessary to evaluate ambulatory surgical patients?

Two hundred twelve consecutive adult patients undergoing a variety of ambulatory surgical procedures were studied prospectively to investigate whether routine preoperative urinalyses, complete blood counts (CBCs), and electrocardiograms (ECGs) were useful in determining the outcomes of their treatments. Urinalyses (U/As) were abnormal in 83 patients (39%); CBCs were abnormal in 19 patients (9%), and ECGs were abnormal in 140 patients (66%). The mean age of the patients was 64 plus or minus 12 years. The majority of patients with abnormalities determined by laboratory tests could have been predicted to have abnormalities on the basis of their histories and physical examinations. In this study, abnormalities indicated by laboratory tests did not influence preoperative cancellations, intraoperative or postoperative complications, or admissions to the hospital from the ambulatory unit after the surgical procedures. We conclude that routine preoperative screening laboratory tests have only a limited value in ambulatory surgical patients and recommend that they be either eliminated or replaced with less costly studies; for example, dipstick urinalyses for urinalyses, spun hematocrits for CBCs, and ECGs should be performed only if indicated by history and physical examination findings or if requested by an anesthesiologist.