Lactase deficiency exists in four distinct forms: primary (the most common), secondary, congenital, and developmental.
Treatment of primary lactase deficieny is indicated only when it manifests as a clinical syndrome of lactose intolerance.
Lactose intolerance is characterised by by gastrointestinal symptoms such as diarrhoea, bloating, and abdominal discomfort. Some patients have systemic symptoms (e.g., headache, poor short-term memory, severe tiredness, joint and/or muscle pain, eczema, mouth ulceration)
Dietary elimination and challenge are generally diagnostic.
Treatment includes reduction or elimination of dietary lactose.
If elimination of lactose is necessary, alternative calcium sources are recommended.
Lactase deficiency is usually primary (hereditary) due to a non-persistence of lactase with an age-related decline that begins after weaning although it is rare before 2 to 3 years of age. This results in hypolactasia (low lactase activity), characterised by reduced lactase (lactase-phlorizin hydrolase enzyme) concentration in the mucosal brush border (microvilli) of the small intestine. Less often lactase deficiency is secondary to small bowel injury: causes include infection (e.g., HIV enteropathy, tropical sprue), systemic conditions (e.g., carcinoid syndrome), chemotherapy and radiotherapy. In infants lactase deficiency is most often secondary to infection (gastroenteritis) or cows’ milk protein allergy. Congenital lactase deficiency is an extremely rare, lifelong disorder characterised by faltering growth and intractable diarrhoea from the first exposure to breast or lactose-containing formula milk. Affected infants have minimal or absent lactase activity. Lactase deficiency is also seen in preterm infants due to the mucosal structure not being developed fully.
Lactose intolerance refers to the development of gastrointestinal and/or systemic symptoms secondary to malabsorption of lactose caused by hypolactasia. Malabsorption of lactose, however, does not always manifest as gastrointestinal symptoms; development of symptoms and symptom severity depend on the amount and rate of lactose reaching the colon, as well as the type and amount of colonic flora.
History and exam
Key diagnostic factors
- presence of risk factors
- symptoms after ingestion of dairy products
- mouth ulceration
- poor short-term memory
- poor concentration
- muscle/joint pain
- faltering growth
Other diagnostic factors
- abdominal pain/discomfort
- skin rashes
- history of asthma
- history of peptic ulcer disease
- history of gastro-oesophageal reflux disorder
- weight loss
- short stature
- progressive disability
- sensory loss
- hair loss
- black, Native American, Asian, Hispanic, or Jewish ethnicity
- adolescence and early adulthood
- family history of lactase deficiency
- comorbid predisposing disease
- history of irritable bowel syndrome diagnosis
1st investigations to order
- trial of dietary lactose elimination
Investigations to consider
- lactose hydrogen breath test
- stool culture
- faecal pH
- faecal reducing substance/sugar
- lactose tolerance test
- small bowel biopsy
- 13C-labelled lactose breath test
demonstrating symptoms of lactose intolerance
- Coeliac disease
- Sucrase-isomaltase deficiency
- Cow's milk protein intolerance
- Guidelines for the investigation of chronic diarrhoea in adults
- Lactose intolerance in infants, children, and adolescents
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