What is your preferred laboratory test to assess treatment response or infection resolution in patients with bacterial pneumonia?

I don't generally check a laboratory test to assess resolution. I go more by their improved clinical status and seeing them get back to baseline oxygen status. If I am trending a WBC or procal, I do like to see it trend down, but it's not the only lab I hang my hat on to decide if someone has resolved. Then I put a 6-week follow-up CXR in a discharge order, but I'm not sure how often that really gets done.

The criteria for transition from IV to PO antibiotics and hospital discharge in CAP are all based on clinical improvement. There are no recommendations for follow-up laboratory studies, which can lag behind clinical resolution and result in increased cost, increased LOS, and additional unnecessary testing. Repeat chest imaging is also not recommended unless the patient is at increased risk for pulmonary malignancy. A 2023 NEJM clinical practice article presents a thorough discussion (File and Ramirez, PMID 37585629).

Oxygen level, vitals

The 2009 British Thoracic Society guidelines for the management of community-acquired pneumonia suggest that chest radiograph and hospitalization be considered for outpatients with pneumonia who fail to improve after 48 hours of treatment.

In practice, I find it helpful to check CT chest for non-resolving pneumonia for those patients not improving in 48-72 hours despite antibiotics and aggressive pulmonary toilet, especially those with new high oxygen requirement. I would look for UIP, NSIP, COOP, pulmonary vasculitis syndromes, etc, and some noninfectious pneumonia would benefit from early initiation of high dose steroids. Pulmonary consultation with assessment of candidacy for bronchoscopy and BAL is helpful in these ca...