Gastro‑oesophageal reflux disease (GORD), also known as acid reflux, is a chronic condition in which the contents of the stomach regurgitate into the oesophagus or larynx. This happens when the lower oesophageal sphincter, the valve between the stomach and oesophagus, is weak or relaxes inappropriately.

The regurgitated liquid usually contains stomach acid and the stomach enzyme pepsin. Unlike the mucosal cells that line the stomach, the mucosal cells that line the oesophagus, larynx and airways are not resistant to acid. Therefore, the stomach acid can inflame and damage the lining of the oesophagus causing oesophagitis, heartburn, sore throat and dysphagia. In the larynx it can cause sore throat and voice disorders. The severity of the symptoms depends on the degree of sphincter dysfunction, the type and amount of fluid brought up from the stomach, and the neutralising effect of saliva.

According to NICE guidance on dyspepsia, GORD is a common condition. About 1 in 5 people are thought to experience at least 1 episode of GORD per week, with 1 in 10 people experiencing symptoms of GORD daily. People of all ages can be affected, including children, but it is more prevalent in adults aged 40 years or older. Severe cases of oesophagitis can cause the formation of oesophageal ulcers that may bleed, causing pain and making swallowing difficult. Repeated episodes of GORD can lead to changes in the cells in the lining of the lower oesophagus, a condition known as Barrett's oesophagus. This condition is estimated to affect 1 in 10 people with GORD. Barrett's oesophagus is characterised by pre‑cancerous changes to the cells lining the oesophagus. These cells have an increased risk of becoming cancerous in time. Conversion of Barrett's oesophagus to oesophageal adenocarcinoma has a lifetime risk of 5% in men and 3% in women (Jankowski 2010).

GORD is normally diagnosed empirically with a trial of proton pump inhibitors or by endoscopy, manometry or pH testing when more serious disease is suspected. It may present with atypical symptoms, including chronic cough, hoarseness, loss of voice, laryngeal pain or ear, and nose and throat symptoms caused by stomach contents reaching the larynx and trachea. This is known as laryngopharyngeal reflux.

Although the presence and quantity of pepsin in saliva may indicate the presence of GORD, there is no consensus in the published literature about what concentration of pepsin would be considered clinically relevant. Published studies have used different pepsin concentrations ranging from 16 ng/ml to 25 ng/ml as a cut‑off value to indicate a clinically significant concentration of pepsin in saliva.