These authors address a real problem: which coughing adults have pneumonia? Unfortunately, after evaluating 2,820 of them – they still don’t really know.
This is an interesting article because it pulls together a symptom profile along with two of the other non-specific inflammatory markers being touted as important diagnostic tools: CRP and procalcitonin. Primary care physicians enrolled adults presenting with acute cough, and used plain radiography as their gold standard for diagnosis of pneumonia.
In short:
- “Symptoms and signs” suggestive of pneumonia (fever, tachycardia, abnormal lung exam) all had positive OR between 2.0 and 5.3, and combined offered an AUC of 0.70.
- Adding CRP as a continuous variable to symptoms and signs gave an OR of 1.2 and increased the AUC to 0.78.
- Adding procalcitonin as a continuous variable to symptoms and signs gave an OR of 1.1 and increased the AUC to 0.72.
Using CRP as a dichotomous cut-off at 30 mg/L, in addition to the independent symptom predictors, gave them the discriminating ability to produce a low, intermediate and high risk group: 0.7%, 3.8%, and 18.2% chance of pneumonia. A high-risk group where fewer than one in five have the disease? The authors recommend consideration of empiric antibiotic therapy in this group, but I prefer their other recommendation to consider radiography as confirmation in this subset. The remainder ought to be candidates for observation, as false positives and harms from additional testing are likely to outweigh true positives.
Again, refuting the terrible JAMA distortion, procalcitonin had no useful discriminatory diagnostic value.