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Introduction ⬇

Lactose intolerance often begins in infancy, with symptoms of diarrhea, vomiting, failure to thrive, and malabsorption. The patient has no symptoms when lactose is removed from the diet. This syndrome is caused by a deficiency of sugar-splitting enzymes (lactase) in the intestinal tract.

This test is actually a GTT done to diagnose intestinal disaccharidase (lactase) deficiency. Glucose is measured, and it is the increase or lack of increase over the fasting specimen that is used for the interpretation. Breath samples reveal increased hydrogen levels, which are caused by lactose buildup in the intestinal tract. Colonic bacteria metabolize the lactose and produce hydrogen gas.

Normal Findings ⬆ ⬇

Change in glucose from normal value >30 mg/dL or >1.7 mmol/L

Inconclusive: 20–30 mg/dL or 1.1–1.7 mmol/L

Abnormal: <20 mg/dL or <1.1 mmol/L

Hydrogen (breath):

Fasting: <5 ppm or <5 × 10−6

After lactose ingestion: <12 ppm or <12 × 10−6 increase from fasting level

Procedure ⬆ ⬇

  1. Draw a blood specimen from a fasting patient. The patient then drinks 50 g of lactose mixed with 200 mL of water (2 g of lactose/kg body weight).

  2. Draw blood lactose samples at 0, 30-, 60-, and 90-minute intervals.

  3. Take breath hydrogen samples at the same time intervals as the blood specimens. Contact your laboratory for collection procedures.

Clinical Implications ⬆ ⬇

  1. Lactose intolerance occurs as follows:

    1. A “flat” lactose tolerance finding (i.e., no rise in glucose) points to a deficiency of sugar-splitting enzymes, as in irritable bowel syndrome. This type of deficiency is more prevalent in Native Americans and people of African, Asian, and Jewish descent.

    2. A monosaccharide tolerance test such as the glucose/galactose tolerance test should be done as a follow-up:

      1. The patient ingests 25 g of both glucose and galactose.

      2. A normal increase in glucose indicates a lactose deficiency.

    3. Secondary lactose deficiency found in:

      1. Infectious enteritis

      2. Bacterial overgrowth in intestines

      3. Inflammatory bowel disease, Crohn disease

      4. Giardia lamblia infestation

      5. Cystic fibrosis of pancreas

  2. The breath hydrogen test is abnormal in the lactose deficiency test because:

    1. Malabsorption causes hydrogen (H2) production through the process of fermentation of lactose in the colon.

    2. The H2 formed is directly proportional to the amount of test dose lactose not digested by lactase.

  3. In diabetes:

    1. Blood glucose values may show increases >20 mg/dL (>1.11 mmol/L) despite impaired lactose absorption.

    2. There may be an abnormal lactose tolerance curve due to faulty metabolism, not necessarily from lactose intolerance.

Interventions ⬆

Pretest Patient Care

  1. Explain test purpose and procedure. The patient must fast for 8–12 hours before the test.

  2. Do not allow the patient to eat dark bread, peas, beans, sugars, or high-fiber foods within 24 hours of the test.

  3. Do not permit smoking during the test and for 8 hours before testing; no gum chewing.

  4. Do not allow antibiotic drugs to be taken for 2 weeks before the test unless specifically ordered.

  5. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Have the patient resume normal diet and activity.

  2. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient appropriately. Patients with irritable bowel syndrome with gas, bloating, abdominal pain, constipation, and diarrhea have lactose deficiency. Restricting milk intake relieves symptoms.

  3. Follow guidelines in Chapter 1 regarding safe, effective, informed posttest care.