Lactase deficiency

Last reviewed: 2 Jan 2023
Last updated: 21 Dec 2022



History and exam

Key diagnostic factors

  • presence of risk factors
  • symptoms after ingestion of dairy products
  • diarrhoea
  • distension
  • lethargy
  • mouth ulceration
  • headache
  • poor short-term memory
  • poor concentration
  • muscle/joint pain
  • eczema
  • faltering growth
More key diagnostic factors

Other diagnostic factors

  • abdominal pain/discomfort
  • borborygmi
  • flatulence
  • skin rashes
  • palpitations
  • history of asthma
  • history of peptic ulcer disease
  • history of gastro-oesophageal reflux disorder
  • nausea
  • vomiting
  • constipation
  • pallor
  • steatorrhoea
  • weight loss
  • short stature
  • progressive disability
  • flushing
  • sensory loss
  • oedema
  • hair loss
Other diagnostic factors

Risk factors

  • black, Native American, Asian, Hispanic, or Jewish ethnicity
  • adolescence and early adulthood
  • family history of lactase deficiency
  • enteritis/gastroenteritis
  • comorbid predisposing disease
  • history of irritable bowel syndrome diagnosis
More risk factors

Diagnostic investigations

1st investigations to order

  • trial of dietary lactose elimination
  • FBC
More 1st investigations to order

Investigations to consider

  • lactose hydrogen breath test
  • stool culture
  • faecal pH
  • faecal reducing substance/sugar
  • lactose tolerance test
  • small bowel biopsy
More investigations to consider

Emerging tests

  • genotyping
  • 13C-labelled lactose breath test

Treatment algorithm


demonstrating symptoms of lactose intolerance



Aasma Shaukat, MD, MPH

Director GI Outcomes Research

Robert M. and Mary H. Glickman Professor of Gastroenterology

Professor of Population Health

New York University Grossman School of Medicine

New York



AS declares that she has no competing interests.


Dr Aasma Shaukat would like to gratefully acknowledge Dr Anton Emmanuel, Dr Mohammad Azam, and Dr Richard J. Farrell, previous contributors to this topic.


AE, MA, and RJF declare that they have no competing interests.

Peer reviewers

Anthony Lembo, MD

Assistant Professor of Medicine

Harvard Medical School

Beth Israel Deaconess Medical Center




AL declares that he has no competing interests.

Michele Di Stefano, MD

Coordinator of the Gastrointestinal Motility Laboratory

University of Pavia

1st Division of Medicine

IRCCS S. Matteo Hospital Foundation




MDS is the author of references cited in this topic.

  • Differentials

    • Coeliac disease
    • Sucrase-isomaltase deficiency
    • Cow's milk protein intolerance
    More Differentials
  • Guidelines

    • Adverse events associated with EGD and EGD-related techniques
    • Guidelines for the investigation of chronic diarrhoea in adults
    More Guidelines
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