To investigate the count of white blood cell (WBC) levels, procalcitonin (PCT), C-reactive protein (CRP) and interleukin-6 (IL-6) in patients with severe pneumonia caused by different pathogens, and to provide a theoretical basis for the diagnosis and treatment of pneumonia.

From October 2014 to March 2017, a total of 78 patients with severe pneumonia treated in the First People’s Hospital of Huizhou City who met the inclusion criteria were randomly divided into 5 groups according to the type of pathogenic bacteria, which were single infection group: fungi group (F), Gram-positive bacteria group (G⁺), Gram-negative bacteria group (G^-) and coinfection group: fungi + Gram-positive bacteria group (F + G⁺), fungi + Gram-negative bacteria group (F + G^-). The levels of PCT, CRP, WBC count and IL-6 were detected and compared, respectively.

There was no significant difference among basic diseases, systolic blood pressure, body temperature, heart rate and erythrocyte sedimentation rate among the five groups (all P > 0.05). There were significant differences in serum PCT and WBC levels among the five groups (F = 9.781, P = 0.007; F = 8.373, P = 0.005). Levels of CRP and IL-6 in each group were with small range of changes, but with no significant difference (F = 1.203, P = 0.115; F = 4.572, P = 0.248).

The low level of PCT and high level of CRP indicate that patients with severe pneumonia are infected by fungal, while the increase of procalcitonin indicates that patients with severe pneumonia are infected by Gram-negative bacilli or with compound infection.