If you’re experiencing cramps, bloating, and diarrhea after drinking milk or eating and drinking milk products, your doctor may want to test you for lactose intolerance. Confirmatory tests measure lactase activity in the body. These tests include:

1. Lactose Intolerance Test
This blood test measures your body’s reaction to a liquid that contains high lactose levels.

2. Hydrogen Breath Test
This test measures the amount of hydrogen in your breath after consuming a drink high in lactose. If your body is unable to digest the lactose, the bacteria in your intestine will break it down instead. The process by which bacteria break down sugars like lactose is called fermentation. Fermentation releases hydrogen and other gases. These gases are absorbed and eventually exhaled. If you aren’t fully digesting lactose, the hydrogen breath test will show a higher than normal amount of hydrogen in your breath.

3. Stool Acidity Test
This test is more often done in infants and children. It measures the amount of lactic acid in a stool sample. Lactic acid accumulates when bacteria in the intestine ferment the undigested lactose.