How to Diagnose Lactase Deficiency With a Blood Test

Lactase deficiency, a common condition around the world, can cause lactose intolerance. You might be wondering if you're lactose intolerant if you experience an upset stomach, gas and diarrhea after consuming dairy products. Your doctor can have your blood tested to see if you do have lactase deficiency, and that can help him rule out other gastrointestinal problems.

Difficulty: Moderately Challenging

Instructions

1. Fast for a minimum of 8 hours before you have your blood drawn.

2. Refrain from strenuous exercise for 8 hours prior to the test.

3. Drink a beverage containing lactose that your doctor gives you in her office.

4. Allow your medical practitioner to draw your blood at intervals your doctor determines.

5. Wait for the lab results. The lab technicians look for glucose in your blood when your doctor orders a lactose intolerance test, because the lactase enzyme in your body breaks lactose down into glucose and galactose.

6. Determine what the test results mean. If your glucose level is higher than 30 milligrams per deciliter (mg/dL) after two hours of drinking the lactose solution, you do not have lactase deficiency. If your glucose level is 20-30 mg/dL, your doctor may order more tests for further information. If your glucose rises to below 20 mg/dL, it clearly indicates an abnormality.

Tips & Warnings

• Each laboratory may view a normal glucose range slightly differently, so discuss what your test results mean with your doctor.
• If your test results are abnormal, get a glucose tolerance test to rule out a problem absorbing glucose.
• You may experience minor to moderate pain during and after the blood draw. Rarely, you may experience bleeding, hematoma or fainting.
• Make sure you see the person who draws your blood remove a clean needle and syringe from its sterile package and wash their hands before drawing your blood. Verify that all their equipment is sterile. Patients have gotten blood infections due to improper hygiene.

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