Chapter 6

• The sensitivity of a diagnostic test is the likelihood that persons with the disease of interest will have positive test results.
• The specificity of a diagnostic test is the likelihood that persons who do not have the disease of interest will have negative test results.
• Positive predictive value measures the likelihood of having the disease of interest among those whose diagnostic test results are positive.
• Negative predictive value is the likelihood of not having the disease of interest among those whose diagnostic test results are negative.
• Likelihood ratios can be used to measure the extent to which the likelihood of the disease of interest is changed by the results of a diagnostic test.
• The area under a receiver operating characteristic (ROC) curve can be used to assess the performance of a diagnostic test.
• Screening for a particular disease is conducted in order to detect the disease at an earlier stage than would occur through routine methods.
• An error in the evaluation of a screening test, known as lead time bias, can occur when persons with disease detected by screening appear to live longer simply because of the earlier recognition of their illnesses.
• An error in the evaluation of a screening test, known as length-biased sampling, can occur when persons with disease detected by screening appear to live longer simply because they have more slowly progressing illnesses.

A 54-year-old high school teacher visited her family practitioner for an annual checkup. She reported no illnesses during the preceding year, felt well, and had no complaints. The hot flashes she had experienced a year ago had resolved without treatment. The physician performed a physical examination, comprising breast, pelvic (including a Papanicolaou smear), and rectal examinations; all were unremarkable. The physician recommended that the patient have a mammogram, which was scheduled for 1 week later.

The results of the mammogram were not normal, and the radiologist suggested that a breast biopsy be performed. The family practitioner notified the patient of the abnormal mammogram and referred her to a surgeon, who concurred that physical examination of the breast was normal. Based on the mammographic abnormality, however, the surgeon and the radiologist agreed that fine-needle aspiration (FNA) of the abnormal breast under radiologic guidance was indicated. Evaluation of the FNA specimen by a pathologist revealed cancer cells, and the patient was scheduled for further surgery the following week.

The practice of clinical medicine is the artful application of science. A seemingly straightforward chain of decisions by the physicians in the Patient Profile ultimately led to the diagnosis of breast cancer and subsequent treatment. In practice, however, the process of clinical reasoning can be extremely complex. Each decision made by the clinicians in the Patient Profile included the possibility that information was incorrect. Sir William Osler eloquently described the difficulties of clinical decision making in 1921:

The problems of disease are more complicated and difficult than ...

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

Subscription Options

AccessPharmacy Full Site: One-Year Subscription

Connect to the full suite of AccessPharmacy content and resources including 30+ textbooks such as Pharmacotherapy: A Pathophysiologic Approach and Goodman & Gilman's The Pharmacological Basis of Therapeutics, high-quality videos, images, and animations, interactive board review, drug and herb/supplements databases, and more.