Function tests

• Suspicion of primary or secondary lactase deficiency
• Suspicion of lactose malabsorption of other origins

Lactose is a disaccharide, consisting of D-glucose and D-galactose. On the brush border membrane of the small intestinal mucosa, there is splitting into monosaccharides, mainly hydrolytically by the enzyme lactase or beta-galactosidase. In case of lactase deficiency, the absorbed lactose amount exceeds hydrolytic capacity, which leads to corresponding clinical symptoms, such as diarrhea, flatulence, winds, stomach cramps.

Glucose

2 ml sodium fluoride blood each, before and 30, 60, 90 and 120 min after lactose administration.

The patient should be empty-stomached.

1. Taking of blood prior to tolerance testing
2. Oral administration of 50 g lactose in 400 ml water or tea, children over the age of 2 get 2 g lactose / kg body weight (maximal 50 g) as a 25 % solution.
3. Further blood samples 30, 60, 90 and 120 min after lactose administration.

Preface:

Newest tests pointed out that there may be discrepancies between subjective symptomatology and factual results of the lactose tolerance test or lactose-H2 breath test.

Normal values:
Blood sugar increase of > 20 mg/dl, no gastrointestinal symptoms

Probable lactose malabsorption:
No glucose increase, relevant gastrointestinal symptoms with diarrhea, stomach cramps and flatulence within 8 hours of test start.

Reasons for lactose malabsorption:
Genetically determined lactase-deficiency (so-called primary lactase deficiency), which manifests in childhood or young adolescent age.

Secondary lactase deficiency as a result of intestinal mucosal damage. In case of Celiac’s disease (or sprue), inevitably a lactose intolerance is also found. Symptomatic lactose malabsorption in connection with other gastrointestinal diseases such as duodenal ulcer, ulcerative colitis, Crohn’s disease, lambliasis and others.

Diabetes mellitus:
In patients with latent or manifest diabetes mellitus, false negative results are to be expected.