Preoperative laboratory testing in patients undergoing elective, low-risk ambulatory surgery.

Over the last 2 decades, the indications for ambulatory surgery have expanded, with an increasing number of surgical procedures performed in the ambulatory setting. Currently 60% to 70% of the surgical procedures performed in the United States each year are performed in the ambulatory setting.1,2 Ambulatory surgical procedures are generally less than 1 to 2 hours in duration, have low expected blood loss and complication rates, minimal expected postoperative care, and are usually performed in patients with no medical problems or with stable chronic medical conditions. As surgical and anesthetic techniques have evolved, evidence-based guidelines regarding preoperative testing have lagged. In the United States, current recommendations for preoperative testing are based on the 2002 Practice Advisory from the American Society of Anesthesiologists (ASA) Task Force on Preanesthesia Evaluation.3 These recommendations represent a synthesis of expert opinion and are not based on a sufficient number of adequately powered and controlled trials. Moreover, there are inconsistencies between authorities, and the language of current recommendations is imprecise. For example, “advanced age” is often used as an indication for testing without a clear minimum age. Table 1 summarizes the recommendations of the ASA,3 the Canadian Anesthesiologists’ Society (CAS),4 and the Ontario Preoperative Testing Group (OPTG).5,6 In addition, recommendations for preoperative testing vary widely on the basis of single-institution studies and systematic reviews.7–10 TABLE 1 Summary of Current ASA, CAS, and OPTG Recommendations for Testing in Patients Undergoing Ambulatory Surgery While the cost of individual tests may be low, the aggregate costs can be substantial.11,12 In the United States, the current estimated cost of preoperative testing is $3 billion to 18 billion annually.7,13,14 On the basis of single-institution studies and literature reviews, many advocate against routine preoperative laboratory testing in asymptomatic and clinically normal patients who are undergoing elective, low-risk surgery.5,7–12,14–17 It also has been shown that abnormal results in testing done before elective low-risk surgery change management in less than 3% of cases.5,11,15 Although these groups advocate against “routine” testing, they fail to outline clear and consistent guidelines or indications for specific tests. Several studies, including 2 randomized controlled trials, have evaluated the elimination of preoperative testing in patients undergoing low-risk surgery and have demonstrated no difference in adverse events.1,17,18 Despite these data, several single-institution studies document overuse of preoperative testing in the low-risk, ambulatory setting.5,11,19 However, the use of preoperative testing has not been studied at the population level. Our study uses the American College of Surgeons National Surgical Quality Improvement Program (NSQIP) database to examine current patterns of preoperative laboratory testing in patients undergoing elective hernia repair, a representative low-risk ambulatory operation. Specifically, we examine preoperative testing in all patients and a subgroup with no NSQIP-measured comorbidities and, therefore, no clear indication for pre-operative testing. Finally, this study identifies factors associated with preoperative laboratory testing and examines 30-day outcomes in tested and untested patients and patients with normal and abnormal test results.