Diagnosis of Lactose Intolerance

How do doctors diagnose lactose intolerance?

To diagnose lactose intolerance, your doctor will ask about your symptoms, family and medical history, and eating habits.

Your doctor may perform a physical exam and tests to help diagnose lactose intolerance or to check for other health problems. Other conditions, such as irritable bowel syndrome, celiac disease, inflammatory bowel disease, or small bowel bacterial overgrowth can cause symptoms similar to those of lactose intolerance.

Your doctor may ask you to stop eating and drinking milk and milk products for a period of time to see if your symptoms go away. If your symptoms don’t go away, your doctor may order additional tests.

Physical exam

During a physical exam, your doctor may

  • check for bloating in your abdomen
  • use a stethoscope to listen to sounds within your abdomen
  • tap on your abdomen to check for tenderness or pain
Doctor talking with a patient.
Your doctor will ask about your symptoms, family and medical history, and eating habits.

What tests do doctors use to diagnose lactose intolerance?

Your doctor may order a hydrogen breath test to see how well your small intestine digests lactose.

Hydrogen breath test

Doctors use this test to diagnose lactose malabsorption and lactose intolerance. Normally, a small amount of hydrogen, a type of gas, is found in your breath. If you have lactose malabsorption, undigested lactose causes you to have high levels of hydrogen in your breath.

For this test, you will drink a liquid that contains a known amount of lactose. Every 30 minutes over a few hours, you will breathe into a balloon-type container that measures the amount of hydrogen in your breath. During this time, a health care professional will ask about your symptoms. If both your breath hydrogen levels rise and your symptoms get worse during the test, your doctor may diagnose lactose intolerance.

February 2018

This content is provided as a service of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health. The NIDDK translates and disseminates research findings through its clearinghouses and education programs to increase knowledge and understanding about health and disease among patients, health professionals, and the public. Content produced by the NIDDK is carefully reviewed by NIDDK scientists and other experts.

The NIDDK would like to thank:
Rachel Fisher, M.S., M.P.H., R.D., NIDDK Office of Nutrition Research