Our colour chart is a simple but sensitive diagnostic tool

Dr Sue Hill, Queen Elizabeth Hospital

Researchers at the Queen Elizabeth Hospital, Birmingham, found that the colour of spit from chronic obstructive pulmonary disease (COPD) patients changed according to the level of infection present.

The researchers found that the colour of patients' spit darkens as the immune system releases its natural defence, white blood cells (neutrophils), to fight infection.

Using this information, they developed a simple chart for quick and easy analysis of spit colour, ranging from cream to dark green.

This was successfully used to identify patients with infection from those who did not - although both groups appeared to have similar symptoms.

The colour chart ranges from one to five, with five indicating extensive bacterial infection.

Major disease

COPD is an umbrella term, which covers a number of well-known lung diseases.

They include chronic bronchitis, emphysema, chronic obstructive airways disease, chronic airways disease, chronic airflow limitation and some cases of chronic asthma.

An estimated 20% of all hospital admission are as a result of COPD.

Dr Sue Hill, a consultant clinical scientist at the Lung Investigation Unit at the Queen Elizabeth Hospital, said: "Our colour chart is a simple but sensitive diagnostic tool which we hope will enable practitioners to make better and more accurate diagnoses and to make more rational use of antibiotics."

Dr John Harvey, of the British Thoracic Society (BTS), said: "COPD is a very serious - but often neglected - lung disease.

"This colour chart provides an accurate yet non-invasive method of diagnosis to ensure a better quality of care for patients."

The research was released at British Thoracic Society's Winter Meeting in London.