A ‘distinctive dark green sputum’ in patients with asthma relates to high total cell count and neutrophilic inflammation and might assist with clinical decision making, research suggests.

An Australian study found a sputum colour score greater or equal to three on the five-point BronkoTest predicted higher total cell counts, neutrophil numbers and proportion.

A high sputum colour score also correlated with high concentrations of the neutrophil-active chemokine CXCL-8 and with the presence of bacterial pathogens.

The researchers, from the Hunter Medical Research Institute at the University of Newcastle, said a sputum colour score cut-off ≥3 could effectively discriminate between asthma with and without neutrophilic bronchitis.

The colour comes from the myeloperoxidase present in the azurophil granules of airway neutrophils. A correlation between sputum colour and CXCL-8 has also been demonstrated in other neutrophilic airway diseases including cystic bronchiectasis and COPD.

“Sputum colour could be used in those who can produce a sample, either spontaneously or with a sputum induction, eliminating the need for further processing,” they said.

They suggested the subgroup of patients with a high likelihood of bacterial presence may also benefit from add-on antibiotic therapy such as azithromycin.

“More investigations are required to ascertain the utility of this approach to determine if sputum colour can guide treatment decisions and /or determine treatment response in clinical practice,” they concluded.