Joshua P. Metlay, MD, PhD; Michael J. Fine, MD, MSc
Metlay JP, Fine MJ. Testing Strategies in the Initial Management of Patients with Community-Acquired Pneumonia. Ann Intern Med. 2003;138:109-118. doi: 10.7326/0003-4819-138-2-200301210-00012
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Published: Ann Intern Med. 2003;138(2):109-118.
The initial management of patients suspected of having community-acquired pneumonia is challenging because of the broad range of clinical presentations, potential life-threatening nature of the illness, and associated high costs of care. The initial testing strategies should accurately establish a diagnosis and prognosis in order to determine the optimal treatment strategy. The diagnosis is important in determining the need for antibiotic therapy, and the prognosis is important in determining the site of care.
This paper reviews the test characteristics of the history, physical examination, and laboratory findings, individually and in combination, in diagnosing community-acquired pneumonia and predicting short-term risk for death from the infection. In addition, we consider the implications of these test characteristics from the perspective of decision thresholds. The history and physical examination cannot provide a high level of certainty in the diagnosis of community-acquired pneumonia, but the absence of vital sign abnormalities substantially reduces the probability of the infection. Chest radiography is considered the gold standard for pneumonia diagnosis; however, we do not know its sensitivity and specificity, and we have limited data on the costs of false-positive and false-negative results. In the absence of empirical evidence, the decision to order a chest radiograph needs to rely on expert opinion in seeking strategies to optimize the balance between harms and benefits. Once community-acquired pneumonia is diagnosed, a combination of history, physical examination, and laboratory items can help estimate the short-term risk for death and, along with the patient's psychosocial characteristics, determine the appropriate site of treatment.
The effects of history and physical examination findings separately and in combination were examined in the ambulatory care setting, where the baseline prevalence of community-acquired pneumonia is 5%. Likelihood ratios derived from were applied to the baseline prevalence by using the Bayes theorem (post-test odds = pretest odds × likelihood ratio). The range of revised probabilities depicted by the width of each bar reflects the range of likelihood ratios observed for these findings. The finding of normal vital signs requires heart rate of 100 beats/min or less, temperature of 37.8 °C or less, and respiratory rate of 20 breaths/min or less .
Step 1 identifies patients in risk class I on the basis of age 50 years or younger and the absence of all comorbid conditions and vital sign abnormalities listed in step 2. For all patients who are not classified as risk class I, the laboratory data listed in step 2 should be collected to calculate a pneumonia severity score. Risk class and recommended site of care based on the pneumonia severity score are listed in the final table. Thirty-day mortality data are based on two independent cohorts of 40 326 patients. For additional information, see reference 97 BP = blood pressure; BUN = blood urea nitrogen.
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Infectious Disease, Pulmonary/Critical Care, Pneumonia.
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