Blog | Friday, December 27, 2013

Admission diagnosis of CAP has a high probability of error

Our residents know that I get excited when they present a patient with a presumed diagnosis of community acquired pneumonia (CAP). First, that is not a diagnosis, but rather a syndrome. Second, in my experience, these patients often have another diagnosis, and represent great diagnostic challenges. My talk on learning how to think like a clinician features at least 3 presentations that started as CAP.

On rounds I often explain why I question the diagnosis. I have developed and learned my own illness script for accepting the presumed diagnosis.

This weekend, as I was thinking about this topic, I remembered this article that I quoted in 2008. Antibiotic Timing and Errors in Diagnosing Pneumonia (article free on the website)

Precise criteria for the diagnosis of pneumonia are not available and had to be developed. We based our criteria on those found in Food and Drug Administration–directed clinical trials. Pneumonia was considered present when the medical record docu- mented the presence of all 3 of the following criteria: (1) the presence of a new or increasing infiltrate by chest radiograph or computed tomographic scan; (2) plus a temperature greater than 38.0°C or less than 35.1°C or a total white blood cell count greater than 109/µL or less than 4.5/μL , or immature polymorphonuclear leukocytes (bands) greater than 15%; and (3) plus 2 of cough, dyspnea, pleuritic chest pain, tachypnea with respirations of 30/min or greater, hypoxia with pulse oximetry of less than 90% or PaO2 of less than 60 mm Hg, auscultatory findings of pneumonia, including rales, dullness of percussion, bronchial breath sounds, or egophony, or newly required mechanical ventilation by either intubation or noninvasive ventilation.

So now I have a clearly defined illness script. Although I would add a relatively short time frame of illness.

Misdiagnosis occurred in large numbers of patients.

A total of 548 patients diagnosed as having CAP were studied (255 in group 1 and 293 in group 2). At admission, group 2 patients were 39.0% less likely to meet predefined diagnostic criteria for CAP than were group 1 patients (odds ratio, 0.61; 95% confidence interval, 0.42-0.86) (P = .004). At discharge, there was agreement between the ED physician’s diagnosis and the predefined criteria for CAP in 62.0% of group 1 and 53.9% of group 2 patients (P = .06) and between the ED physician’s admitting diagnosis and that of the discharging physician in 74.5% of group 1 and 66.9% of group 2 patients (P = .05). The mean (SD) TFAD was similar in group 1 (167.0 [118.6] minutes) and group 2 (157.8 [96.3] minutes).

On rounds, CAP gives us a chance to teach the diagnostic process. CAP is not a diagnosis, but rather a suggestion. We should never accept the diagnosis until we carefully consider whether the illness script meets the problem representation. We must remain skeptical about this (and many other) diagnoses.

db is the nickname for Robert M. Centor, MD, FACP. db stands both for Dr. Bob and da boss. He is an academic general internist at the University of Alabama School of Medicine, and is the Associate Dean for the Huntsville Regional Medical Campus of UASOM. He also serves as a frequent ward attending at the Birmingham VA Hospital. This post originally appeared at his blog, db's Medical Rants.