In the previous 2 chapters (Chapter 16, The Process of Diagnosis, and Chapter 17, Differential Diagnosis), we explained the process of diagnosis, the way diagnostic test results move clinicians across the test threshold and the therapeutic threshold, and how to use studies to help obtain an accurate pretest probability. In this chapter, we explain how to use an article that addresses the ability of a diagnostic test to move clinicians toward the extremely high (ruling in) and extremely low (ruling out) posttest probabilities they seek. Later in this book, we explain how to use articles that integrate a number of test results into a clinical prediction rule (Chapter 19.4, Clinical Prediction Rules).
CLINICAL SCENARIO How Can We Identify Dementia Quickly and Accurately?
You are a busy primary care practitioner with a large proportion of elderly patients in your practice. Earlier in the day, you saw a 70-year-old woman who lives alone and has been managing well. On this visit, she informed you of a long-standing problem, joint pain in her lower extremities. During the visit, you get the impression that, as you put it to yourself, “she isn't quite all there,” although you find it hard to specify further. On specific questioning about memory and function, she acknowledges that her memory is not what it used to be but otherwise denies problems. Pressed for time, you deal with the osteoarthritis and move on to the next patient.
That evening, you ponder the problem of making a quick assessment of your elderly patients when the possibility of cognitive impairment occurs to you. The Mini-Mental State Examination (MMSE), with which you are familiar, takes too long. You wonder if there are any brief instruments that allow a reasonably accurate rapid diagnosis of cognitive impairment to help you identify patients who need more extensive investigation.
You formulate the clinical question, “In older patients with suspected cognitive impairment, what is the accuracy of a brief screening tool to identify patients who need more extensive investigation for possible dementia?” To conduct a rapid and specific search, you access the PubMed Clinical Queries page (see Chapter 5, Finding Current Best Evidence). Typing in the search terms “identify dementia brief MMSE,” you select “diagnosis” as the clinical study category and “narrow” as the scope of the filter. This search strategy yields 8 citations.
You survey the abstracts, looking for articles that focus on patients with suspected dementia and report accuracy similar to your previous standard, the MMSE. An article that reports results for an instrument named Six-Item Screener (SIS) meets both criteria.1 You retrieve the full-text article electronically and start to read it, hoping its methods and results will justify using the instrument in your office.
How Serious Is the Risk of Bias?
Box 18-1 summarizes our Users' Guides for ...