Table 1.
Summary of tests for lactose malabsorption and lactose tolerance [25].
| H2-Breath Test [17,45] |
Lactose Tolerance Test [46] |
Genetic Test [3,12] |
Lactase Activity at Jejunal Brush Border [43,44] |
|
|---|---|---|---|---|
| Test principle | Increase of H2 in respiratory air after lactose challenge | Increase of blood sugar after lactose challenge | Genetic-13910C/T polymorphism | Enzymatic activity of lactase enzyme in biopsy sample |
| Cut off | >20 ppm within 3 h | <1.1 mmol/L within 3 h | C:C13910 lactase non-persistence | <17–20 IU/g |
| Availability | Good | Excellent | Variable | Rare |
| False positives (incorrect diagnosis) | Rapid GI-transit, small-intestinal bacterial overgrowth | Rapid GI-transit, impaired glucose tolerance | Rare (<5%) in Caucasians | Probably rare |
| False negatives malabsorption wrongly excluded | Non-H2-producers. Full colonic adaptation | Fluctuations in blood sugar | All causes of secondary lactose malabsorption | Patchy enzyme expression |
| Secondary causes | Cannot be excluded, kinetic of H2-increase can be suggestive | Cannot be excluded | Cannot be excluded | Can be excluded (histopathology at same procedure) |
| Symptom assessment | Possible | Possible | Not possible | Not possible |
| Comment | Method of choice for assessment of lactose malabsorption and intolerance | Rarely performed due to inferior sensitivity and specificity | Definitive in Caucasians. Less in other populations. Not suitable in secondary lactase deficiency. | Reference standard for detection of lactase deficiency (primary or secondary) |
| Cost | Low | Lowest | High | Highest |