In the breath test, a peak rise in hydrogen content of 12 parts per million over the fasting (pre-test) level is considered positive.

In the blood test, a rise in plasma glucose of more than 30 mg/dl within 2 hours of ingesting the lactose is considered normal. A rise of 20-30 mg/dl is inconclusive. A rise of less than 20 mg/dl is abnormal.

Note: mg/dl = milligrams per deciliter

• Lactase deficiency

An abnormal test should be followed by a glucose tolerance test to exclude an abnormality in absorption of glucose before concluding that there is a lactase deficiency.