Lactose intolerance testing

There are a number of lactose intolerance tests available.
There are a number of lactose intolerance tests available.

Lactose intolerance is the inability of the body to digest a sugar called lactose that is found in milk and dairy products.

It is fairly common, with certain ethnic groups affected more than others, and males affected more than females. Under normal conditions dietary lactose is broken down by an enzyme present in the small intestine, called lactase into simpler sugars called glucose and galactose.

People who are lactose-intolerant do not produce enough of this enzyme to break down lactose. The undigested lactose sits in the gut, causing gas, feelings of bloatedness and abdominal cramps. People can also present with diarrhoea in the event of the small intestine unable to absorb the dietary lactose.

What happens when someone has lactose intolerance?

People with lactose intolerance may present with a variety of symptoms. The symptoms are dependant on the amount of dairy product intake and the amount of lactase that the body produces.

Symptoms can manifest within 30 minutes to 2 hours after eating with a person experiencing nausea, stomach cramps, bloating, gas and diarrhoea. Although lactose intolerance is very common, it is important that a person seek medical advice to confirm the diagnosis, as there are many other conditions that share similar symptoms to it.

How do doctors diagnose lactose intolerance?

If lactose intolerance is suspected, your doctor will take a detailed medical history focusing on family history, past history, medications and other pertinent issues. If lactose intolerance is suspected, a lactose-tolerance test, hydrogen-breath test or in the case of a child a stool-acidity test will be carried out.

A lactose tolerance test measures the ability of the intestines to digest lactose. It is used to diagnose a deficiency of the intestinal lactase enzyme. Although there are several ways to document lactose intolerance, the two common tests include the non -invasive hydrogen breath test and the lactose tolerance test.

The preferred, non-invasive method is the measurement of the breath hydrogen content. Normally very little hydrogen gas is detectable in the breath of an individual. In the case of undigested lactose in the colon, bacteria break down the lactose, producing hydrogen-like gases, which can be analysed. The test includes a pre-meal hydrogen breath test followed by an intake of food or drink containing lactose. After a while the breath test is repeated. The diagnosis is then confirmed or excluded by comparing the hydrogen content of the pre and post lactose meal. 

If this test is not available, blood samples are drawn from a vein on the inside of the elbow or the back of the hand at various times to measure the amount of glucose, a product of lactose breakdown, in your blood. These blood samples are taken at baseline, that is immediately prior to the test, and then at various times after drinking a lactose solution (usually 30, 60, and 120 minutes). A rise in the plasma glucose of more than 1.65 mmol/l within 2 hours of ingesting the lactose is considered normal. A rise of 1.1-1.65 mmol/l is inconclusive, whilst a rise of less than 1.1 mmol/l is considered abnormal. 

In the case of suspected lactose intolerance in an infant or child a stool-acidity test is carried out. The undigested lactose undergoes fermentation by colonic bacteria, creating lactic acid and other short-chain fatty acids, which can be detected in a stool sample by measuring the amount of acid in the stool. 

Doctors can also perform an endoscopy to confirm the presence of the enzyme lactase. During this procedure, the inside of the intestines can be viewed by inserting a long tube with a light and tiny camera at its end through the mouth or anus. Tissue samples and pictures of your gut can be taken in this way in order to confirm a diagnosis.

How to prepare for the test

An 8-hour fast and the avoidance of strenuous exercise is recommended before the test. The breath sample is collected in either a special bag or syringe, and is not associated with any pain or discomfort. The blood test however, requires the insertion of a needle to draw blood, and is associated with a stinging sensation at the site. 

Image credit: iStock

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