Excerpt from Preoperative Testing

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Medical consultants are generally asked to assess preoperative risk in most patients who are to undergo surgery. The focus of discussion in this article applies to healthy people who are to undergo an elective surgical procedure.

Despite a low risk of perioperative complications, the use of laboratory tests before surgery became ingrained in clinical practice not only across the United States but also across the world in the latter half of the 20th century. At that time, clinicians thought it logical to order tests to detect abnormalities that might lead to increased morbidity or mortality in the perioperative period. Despite its widespread use, however, systematic evaluations of the clinical effectiveness and cost-effectiveness of routine laboratory testing were often lacking.

In the early and mid 1980s, several investigators published a number of papers demonstrating that routine preoperative testing was not cost-effective and did not benefit the patient. For example, in the mid 1980s, Kaplan and colleagues, in a retrospective review of the charts of 2000 patients who underwent elective surgery, demonstrated that 60% of these patients had laboratory tests ordered for no apparent reason, and that only 0.22% of the abnormal results influenced preoperative management. In another study, Turnbull and colleagues reviewed the charts of 2570 patients undergoing elective surgery, finding that only 104 of 5003 laboratory test results were abnormal and significant, and that only 4 patients would have benefited from "routine" laboratory testing.

To compound the problem, it appears that physicians are poor at evaluating the tests ordered. For example, in a study in which the records of 3782 elective surgery patients were reviewed, only 10 of 160 patients with abnormal test results were treated for such abnormalities. The lack of treatment of identified abnormalities therefore raises the issue of increased legal liability.

In the last 20 years, a progressive challenge to the use of gratuitous routine laboratory testing has developed, especially within the environment of cost-containment and managed care. What, then, should physicians do? A good history and physical examination followed by a review of a patient's chart are undoubtedly the most important routine tests needed.

For example, Narr and colleagues reviewed the charts of 1044 healthy patients who did not undergo any preoperative laboratory testing before their elective surgeries. These patients did not experience any significant perioperative morbidity or mortality. The use of previous laboratory results, performed within 4 months before elective surgery, was supported by a study in which 7549 laboratory results of 1109 patients were reviewed. This study showed that 47% of the laboratory test results duplicated those obtained within 1 year. Of the 3096 normal laboratory test results, only 13 (0.4%) repeated values were abnormal, most of which could have been predicted on the basis of patient history and physical findings.

Furthermore, 5% of healthy people have abnormal test results. This is due to arbitrary cut points that define the range of normal laboratory values to include 2 standard deviations with a 95% confidence interval. For example, the chance that the results of 1 of the 6 tests included in a basic metabolic profile will be abnormal is 26%; hence, the predictive value of the test will be low, especially if the prevalence of the disease is low. For example, based on the Bayes theorem, the positive predictive value of an abnormal hemoglobin test finding is 16.1%, since the prevalence of anemia in healthy individuals is approximately 1%. Accordingly, such abnormal laboratory values, with very low predictive values, may result in further unnecessary workup and delays in surgery.

In a review of studies of routine preoperative testing by Smetana et al (2003), the positive likelihood ratio was modest (>3) for hemoglobin, electrolytes, and renal dysfunction but had a low impact for change on preoperative management. Normal test results did not reduce the likelihood of postoperative complications. In a recent single center study, the incidence of unindicated preoperative screening tests was found to be more than 50%, but it did not add to any benefit to support this persistence of unwarranted testing.

Advancing age, especially older than 70 years, is associated with increased hospital stay and perioperative morbidity and mortality. However, most people in this age group have comorbid conditions, and it remains unclear if complications are secondary to comorbid conditions or age itself.

Contrary to the common belief, obesity does not increase postoperative complications. In a prospective cohort of 6336 patients undergoing general elective surgery, Dindo et al (2003) did not find obesity to be a risk factor for the development of postoperative complications.

For excellent patient education resources, visit eMedicine's Procedures Center. Also, see eMedicine's patient education article Understanding X-rays.

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