Lactose tolerance test

Overview

A lactose tolerance test is a medical test that checks how well your body digests lactose, a sugar found in milk and dairy products. It helps doctors find out if you have lactose intolerance, which means your body cannot break down lactose properly.

Lactose intolerance is very common worldwide – about 68% of people have some degree of it. The test is done frequently when someone has symptoms after eating dairy.

The test is used for people of any age who have symptoms like bloating, gas, or diarrhea after eating dairy. It is more common in adults and in people of Asian, African, or Hispanic heritage.

Symptoms

Common symptoms

• Bloating or swelling in the belly
• Gas and flatulence
• Stomach cramps or pain
• Diarrhea or loose stools
• Nausea

Symptoms in children

• Same symptoms as adults, plus irritability after eating dairy
• Slow weight gain or growth
• Foul-smelling stools

Symptoms in older adults

• Symptoms may be confused with other digestive disorders
• Diarrhea can lead to dehydration more easily
• May also have less appetite

Causes

Main causes

• Lactase deficiency: your body does not make enough of the enzyme that breaks down lactose
• Genetic lactose intolerance: runs in families, more common in certain ethnic groups
• Secondary lactose intolerance: caused by damage to the small intestine from infections, surgery, or diseases like celiac disease

Risk factors

• Family history of lactose intolerance
• Being of Asian, African, Hispanic, or Native American descent

When to see a doctor

See a doctor urgently if:

• Severe pain or swelling in your belly
• Blood in your bowel movements
• Unexplained weight loss or loss of appetite

Book a routine appointment if:

• You often get bloating, gas, or diarrhea after eating dairy products
• Symptoms keep coming back and affect your quality of life

Diagnosis

Your doctor will first ask about your symptoms and when they happen. If lactose intolerance is suspected, they may recommend a lactose tolerance test, often a hydrogen breath test.

Tests that may be done

• Hydrogen breath test: after drinking a lactose solution, your breath is tested for hydrogen gas, which indicates undigested lactose.
• Lactose tolerance blood test: blood samples are taken after drinking lactose to see how much sugar gets into your blood.
• Stool acidity test: mainly used for infants and young children to check for undigested lactose.

What to expect at your appointment

You will drink a sweet liquid containing lactose. Then over the next 2 to 3 hours, you will give breath or blood samples at set times. The test is painless but may cause temporary discomfort. You should not eat or drink anything except water for about 8 to 12 hours beforehand.

Treatment

Treatment for lactose intolerance focuses on managing symptoms through diet. Most people can find a balance that works for them.

Self-care at home

• Limit the amount of dairy you eat at one time
• Choose lactose-free or low-lactose milk and dairy products
• Try taking lactase enzyme pills or drops before eating dairy (check with your doctor or pharmacist first)
• Keep a food diary to see which foods cause symptoms

Medical treatments

Your doctor may suggest a temporary elimination diet to see if symptoms improve, or recommend over-the-counter lactase enzyme supplements. If you have secondary lactose intolerance from another condition, treating that condition often helps. Always discuss any supplement with your healthcare provider.

When is surgery considered?

Living with this condition

Many people with lactose intolerance lead perfectly normal lives by making small diet changes. You do not have to avoid all dairy – some types like hard cheese or yogurt may be easier to digest.

Lifestyle tips

• Read food labels carefully – lactose is added to many packaged foods.
• Try smaller servings of dairy and see how much you can handle.
• Ask your doctor if you need calcium or vitamin D supplements if you cut out dairy.

Diet and exercise

A healthy diet without dairy is possible. Get calcium from leafy green vegetables, almonds, tofu, and fortified plant milks. Regular exercise is fine and can help with digestion.

Mental health and emotional wellbeing

Having to change your diet can feel frustrating or socially awkward at first. Give yourself time to adjust – most people find new habits quickly and feel better without the uncomfortable symptoms.

Prevention

Primary lactose intolerance (caused by genetics) cannot be prevented. You are born with the tendency. Secondary lactose intolerance may be prevented by treating the gut condition that causes it, such as avoiding gluten if you have celiac disease. But you cannot always prevent damage to the intestine.

Screening programmes

There is no routine screening test for lactose intolerance. Testing is done only if you have symptoms.

Complications

If left untreated

• Continuing discomfort such as bloating and diarrhea
• Possible poor absorption of calcium and vitamin D if you avoid all dairy without replacing them
• In very rare cases, severe dehydration from persistent diarrhea

Long-term outlook

The outlook is excellent. With simple dietary changes, most people with lactose intolerance manage their symptoms well and live a healthy, full life. It is not a serious or life-threatening condition.

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