To help diagnose lactose intolerance in individuals who have difficulties digesting dairy products, or sometimes as part of an investigation of malabsorption conditions
When you have symptoms such as abdominal pain, bloating, gas, and diarrhoea starting within a few hours after consuming milk and other dairy products
A series of breath samples exhaled into a collector, or a series of blood samples drawn from a vein in your arm
Overnight fasting is required; nothing but water is permitted. Avoid strenuous activities and smoking several hours before testing. You may be instructed to brush your teeth and/or rinse your mouth with water prior to and during the breath test.
Lactose tolerance tests measure hydrogen in the breath or changes in the level of glucose in the blood after a person is given a drink containing a standard amount of lactose, thus determining whether the individual is capable of digesting lactose.
Lactose is a sugar with a complex structure. It is a disaccharide, which means it is composed of two simple sugars joined together. Lactose is found in milk and many other dairy products. Before it can be absorbed and used by the body, it must be broken down into its two simpler sugars, glucose and galactose (monosaccharides). This digestion step is performed by lactase, an enzyme produced by cells lining the small intestine.
If an individual does not produce enough lactase (lactase deficient), then undigested lactose passes through the small intestine to the large intestine, where bacteria break it down, producing hydrogen gas and lactic acid. This process can cause the affected person to experience abdominal pain and bloating, flatulence, and diarrhoea within 30 minutes to 2 hours of consuming milk or other dairy products.
There are 2 types of lactose intolerance.
1. Primary- when your body just doesn’t produce much lactase
Almost all babies are born with the ability to digest lactose, but lactase production normally decreases as an individual ages. About 65-70% of the world's population develops some degree of lactose intolerance by the time they reach adulthood. The intolerance can vary by race and ethnicity, with about 90-95% of northern Europeans retaining their ability to digest lactose and 95-100% of Asians and Native Americans becoming lactose intolerant.
2. Secondary-when the lining of your gut is damaged and temporarily doesn’t produce lactase. This can be produced by any condition that causes damage and irritation to the gut such as gastroenteritis. More serious conditions such as Crohn’s disease, coeliac disease and alcoholism can also cause a secondary intolerance.
In the UK, most cases of lactose intolerance are secondary and are as a result of another illness or condition.
Tests of lactose intolerance are often not necessary. If a doctor suspects a patient has lactose intolerance, then a trial of a lactose free diet may be recommended. If the symptoms improve after 5-7 days of avoidance of lactose-containing foods then the patient will probably not need to have any further tests.
Two different types of lactose tolerance tests are available. They both involve the collection of a fasting sample. The person tested is given a liquid to drink that contains a standard amount of lactose. A series of timed samples is then collected and tested.
Hydrogen breath test
This is the most commonly requested test used to detect and diagnose lactose intolerance. This test measures hydrogen gas in breath samples. With lactose intolerance, undigested lactose reaches the large intestine and is broken down by bacteria, producing excess hydrogen gas. The hydrogen gas enters the circulation and is eventually exhaled by the lungs. This is a simple and non-invasive test to perform.
Lactose tolerance blood test
This test is sometimes used to help diagnose lactose intolerance. This test measures the glucose concentration in the blood samples. It detects the conversion of the ingested lactose into glucose and galactose.
Though these tests are listed as such most laboratories do not offer them routinely. Clinicians mostly suggest a lactose free diet to diagnose this condition.