There are several tests and procedures for clinically diagnosing milk intolerance. These tests and procedures can all be performed at a physician’s office or a hospital on an outpatient basis. The need for these tests often depends on the severity of the condition. Or, the physician may need to exclude a more serious type of condition that shares similar symptoms (e.g., viral flu).

Many people who self-diagnose milk intolerance end up making the wrong diagnosis. Individuals who suspect milk intolerance should not underestimate the value of visiting a physician and receiving formal testing. The tests and procedures most often used include:

• Elimination diet. Involves the removal of foods that contain lactose from a patient’s diet to see if milk intolerance symptoms persist. This should be done under the guidance of a physician or a registered dietitian. People who attempt to self-diagnose milk intolerance often overlook foods that contain milk and fail to remove them from their diet. Many people also conduct the diet for an inadequate period of time to gather conclusive results.
  
  
• Lactose intolerance test. Measures blood glucose (blood sugar) levels for signs that indicate milk intolerance. To begin the test, the patient is given a lactose-loaded drink. Several blood samples are then taken from the patient over the next two hours. The amount of glucose found in the blood samples indicates how well the patient’s body is able to digest lactose. The patient will be required to not eat before the test. This type of test is not normally given to infants and young children because of safety concerns involving a high-lactose drink.
  
  
• Hydrogen breath test. Measures whether there is an abnormal amount of hydrogen in the breath. Normally hydrogen cannot be detected in the breath. However, people with milk intolerance may have it in their breath after ingesting lactose. Undigested lactose in the colon ferments as a result of the bacteria present there, producing several gases, including hydrogen. The hydrogen is absorbed from the intestines into the bloodstream, where it travels to the lungs.
  
  The test results can be affected by certain foods, medications or cigarettes. The consumption of a high-lactose drink makes this test unsafe for young children or infants, but can be safely used on older children.

• Stool acidity test. Measures the amount of acid present in the stool. Lactic acid and other fatty acids are created when undigested lactose ferments in the colon. These then pass into the stool. The test may also look for glucose, which indicates the presence of unabsorbed lactose in the colon. This type of test is safe to perform on patients of all ages, including infants and young children.
  
  
• Milk challenge. Simple method often used to self-diagnose milk intolerance. The challenge consists of a period of fasting (usually overnight) followed by the consumption of a single glass of milk. No other types of food or drink are consumed for the next three to five hours. If a person has a milk intolerance, symptoms should appear within several hours.