C-reactive protein influences the doctor’s degree of suspicion of pneumonia in primary care: a prospective observational study

BACKGROUND: In primary care, the diagnosis of pneumonia is often based on history and clinical examination alone. However, a previous study showed that the general practitioner’s degree of suspicion correlates well with findings on chest X-ray, when the C-reactive protein (CRP) value is known. OBJECTIVES: The present study aimed to investigate to what extent the physician’s degree of suspicion is affected by the CRP level when community-acquired pneumonia is suspected in primary care. METHODS: A prospective observational study was conducted at five primary health care centres in Sweden between October 2015 and December 2017. Adult patients (n = 266) consulting their health care centre with symptoms of lower respiratory tract infection, where the physician suspected pneumonia, were included consecutively. Anamnestic information and findings from clinical examination were documented in a case report form. All patients were tested for CRP. The physicians rated their degree of suspicion as ‘unsure,’ ‘quite sure,’ and ‘sure’ before and after the CRP result. RESULTS: The degree of suspicion of pneumonia changed in 69% of the cases; most often to a lower degree (40%). In 28% of the cases, there was no longer any suspicion of pneumonia after CRP. CONCLUSION: Our results indicate that CRP testing highly influences the physician’s degree of suspicion of pneumonia in primary care and that it seems to be of most value when not sure of the diagnosis.