Lactose Intolerance Workup

Author: Praveen K Roy, MD, AGAF; Chief Editor: Julian Katz, MD more...

Updated: Jun 16, 2011

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Laboratory Studies
Imaging Studies
Other Tests
Procedures
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Laboratory Studies

Lactose tolerance test

This test is rarely done in clinical practice.

Measure serial blood glucose levels after an oral lactose load. A fasting serum glucose level is obtained, after which 50 g of lactose is administered.^[10]Measure the serum glucose level at 0, 60, and 120 minutes.

The lactose tolerance test has a sensitivity of 75% and a specificity of 96%.

False-negative results occur in presence of diabetes and small bowel bacterial overgrowth. Abnormal gastrointestinal emptying can also affect the results of the lactose tolerance test.^[11]

The diagnosis is confirmed if the serum glucose level fails to increase by 20 g/dL above baseline.

Milk tolerance test

Administer 500 mL of milk and measure the blood glucose level.

An increase of less than 9 mg/dL indicates lactose malabsorption.^[12]

Imaging Studies

Imaging tests are not helpful in the diagnosis of primary lactose intolerance, but they may be helpful for excluding secondary causes.

Breath hydrogen test

This is the diagnostic test of choice.

Subjects are administered lactose after an overnight fast, after which expired air samples are collected before and at 30-minute intervals for 3 hours to assess hydrogen gas concentrations.

A rise in breath hydrogen concentration greater than 20 parts per million over the baseline after lactose ingestion suggests lactase deficiency.^[10]

Dietary elimination

Resolution of symptoms with elimination of lactose-containing food products and resumption of symptoms with the reintroduction are findings suggestive of lactose intolerance.^{[13, 14]}

Small bowel biopsy

This is the criterion standard; however, it is invasive and rarely performed. A major advantage is that it provides definitive information.

Biopsy samples from the small bowel are assayed for lactase activity. The biopsy results may be normal if deficiency is focal or patchy.

This is not readily available and is not usually necessary.

Proceed to Treatment & Management

Contributor Information and Disclosures

Author

Praveen K Roy, MD, AGAF Gastroenterologist, Oschner Clinic Foundation; Clinical Assistant Professor of Medicine, University of New Mexico School of Medicine; Comments and Criticisms Editor, Cochrane Colorectal Cancer Group; Adjunct Associate Research Scientist, Lovelace Respiratory Research Institute; Editor-in-Chief, The Internet Journal of Gasteroenterology; Editorial Board, Signal Transduction Insights; Editorial Board, The Internet Journal of Epidemiology; Editorial Board, Gastrointestinal Endoscopy Review Letter

Praveen K Roy, MD, AGAF is a member of the following medical societies: American College of Gastroenterology, American Gastroenterological Association, and American Society of Gastrointestinal Endoscopy

Disclosure: Nothing to disclose.

Coauthor(s)

Abhishek Choudhary, MD Resident Physician, Department of Internal Medicine, University Hospital of Missouri-Columbia

Abhishek Choudhary, MD is a member of the following medical societies: American College of Physicians

Disclosure: Nothing to disclose.

Mohamed Othman, MD Resident Physician, Department of Internal Medicine, University of New Mexico School of Medicine

Disclosure: Nothing to disclose.

Homayoun Shojamanesh, MD Former Fellow, Digestive Diseases Branch, National Institutes of Health

Homayoun Shojamanesh, MD is a member of the following medical societies: American College of Gastroenterology, American Gastroenterological Association, and American Society for Gastrointestinal Endoscopy

Disclosure: Nothing to disclose.

Jack Bragg, DO Associate Professor, Department of Clinical Medicine, University of Missouri School of Medicine

Jack Bragg, DO is a member of the following medical societies: American College of Osteopathic Internists and American Osteopathic Association

Disclosure: Nothing to disclose.

Gautam Dehadrai, MD Department Chair, Section Chief, Department of Interventional Radiology, Norman Regional Hospital

Gautam Dehadrai, MD is a member of the following medical societies: American College of Radiology, Medical Council of India, and Radiological Society of North America

Disclosure: Nothing to disclose.

Showkat Bashir, MD Assistant Professor, Department of Medicine, Division of Gastroenterology, George Washington University, Washington, DC

Showkat Bashir, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, and American Medical Association

Disclosure: Nothing to disclose.

Specialty Editor Board

Ronnie Fass, MD Chief of Gastroenterology, Southern Arizona VA Health Care System; Professor of Medicine, Division of Gastroenterology, University of Arizona School of Medicine

Ronnie Fass, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians-American Society of Internal Medicine, American Gastroenterological Association, American Motility Society, American Society for Gastrointestinal Endoscopy, and Israel Medical Association

Disclosure: Takeda Pharmaceuticals Grant/research funds Conducting research; Takeda Pharmaceuticals Consulting fee Consulting; Takeda Pharmaceuticals Honoraria Speaking and teaching; Vecta Consulting fee Consulting; XenoPort Consulting fee Consulting; Eisai Honoraria Speaking and teaching; Wyeth Pharmaceuticals Conducting research; AstraZeneca Grant/research funds Conducting research; Eisai Consulting fee Consulting

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Douglas M Heuman, MD, FACP, FACG, AGAF Chief of Hepatology, Hunter Holmes McGuire Department of Veterans Affairs Medical Center; Professor, Department of Internal Medicine, Division of Gastroenterology, Virginia Commonwealth University School of Medicine

Douglas M Heuman, MD, FACP, FACG, AGAF is a member of the following medical societies: American Association for the Study of Liver Diseases, American College of Physicians, and American Gastroenterological Association

Disclosure: Novartis Grant/research funds Other; Bayer Grant/research funds Other; Otsuka Grant/research funds None; Bristol Myers Squibb Grant/research funds Other; Scynexis None None; Salix Grant/research funds Other; MannKind Other

Alex J Mechaber, MD, FACP Senior Associate Dean for Undergraduate Medical Education, Associate Professor of Medicine, University of Miami Miller School of Medicine

Alex J Mechaber, MD, FACP is a member of the following medical societies: Alpha Omega Alpha, American College of Physicians-American Society of Internal Medicine, and Society of General Internal Medicine

Disclosure: Nothing to disclose.

Chief Editor

Julian Katz, MD Clinical Professor of Medicine, Drexel University College of Medicine

Julian Katz, MD is a member of the following medical societies: American College of Gastroenterology, American College of Physicians, American Gastroenterological Association, American Geriatrics Society, American Medical Association, American Society for Gastrointestinal Endoscopy, American Society of Law, Medicine & Ethics, American Trauma Society, Association of American Medical Colleges, and Physicians for Social Responsibility

Disclosure: Nothing to disclose.

References

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