Conclusion
As l-lactate in sputum is closely correlated to sequestration of neutrophils in the lungs, l-lactate is a marker for local inflammation in LRTI and a potential biomarker in clinical management of LRTI. On expectorated sputum, d-lactate had no clinical relevance.
Methods
Patients with acute LRTI were prospectively recruited. Sputum samples were collected and analysed for neutrophil count, l-lactate and d-lactate. We had data on pathogens from sputum cultures and polymerase chain reaction (PCR) (atypical bacteria, virus) and C-reactive protein (CRP) from blood.
Results
In 44 sputum samples from 32 patients, the median (interquartile range (IQR)) sputum neutrophil granulocyte count was 0.615 × 107 cells/mL (0.236-1.575). The sputum neutrophil granulocyte count was associated with sputum l-lactate (p = 0.011) and CRP (p = 0.018), but not with d-lactate (p = 0.177). There was a strong association between sputum d-lactate and l-lactate (p < 0.0001).