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Lactose tolerance serum test
This is a test to see whether your body is able to break down lactose. Lactose is a type of sugar found in milk, cheese, ice cream, and other dairy products. Lactase, an enzyme in your stomach, breaks down lactose into 2 simple sugars: glucose and galactose. Within 2 hours of eating, your blood glucose level should rise. This blood test measures the increase.
You may need this test if you have symptoms of lactose intolerance. Symptoms include:
Gas
Stomach cramps
Bloating
Nausea
Diarrhea, especially after you eat or drink milk and other dairy products, such as ice cream and cheese
Lactose intolerance is more common in people of certain ethnic backgrounds. These include African, Hispanic/Latino, American Indian, and Asian.
You also might have this test if you have an intestinal problem like inflammatory bowel disease or a malabsorption syndrome like short gut syndrome. Infants who are not gaining enough weight may also have this test.
You may also have a lactose hydrogen breath test, another way to measure your body's ability to break down lactose. This test measures the amount of hydrogen in your breath. If you are unable to digest lactose, your breath will have a high amount of hydrogen.
If this test is for your child, they may have stool tested for acidity. A child may have glucose in their stool because of undigested lactose.
You may also have a glucose tolerance test. Glucose tolerance is used to diagnose diabetes. When you have diabetes, either your pancreas does not make enough of the hormone insulin to break down sugar or the cells in your body that use insulin become more resistant to it.
Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.
If your glucose levels increase to greater than 20 milligrams per deciliter (mg/dL) after drinking the lactose, you likely don't have lactose intolerance or a problem with absorption.
If your glucose levels don't rise after drinking the lactose, you may be lactose intolerant or have a problem with absorption.
This test is done with 4 blood samples, which are drawn through a needle from a vein in your arm. Your healthcare provider will take the first sample before you drink a dose of lactose, usually 50 grams of lactose diluted in 200 milliliters of water. The other blood samples are taken at specific time intervals after you drink the lactose—at 30 minutes, 1 hour, and 2 hours.
Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore.
Your results might be affected if you:
Exercise strenuously before testing
Eat or drink before testing, or chew gum
Have diabetes
Smoke
Take antibiotics within 2 to 4 weeks of your test
Have a malabsorption syndrome
You will need to fast (not eat or drink anything except for water) for about 8 to 12 hours before the test. Also don't smoke or exercise for at least 8 hours before you have this test. Don't take antibiotics for 1 month before this test. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.