Brief characterisation of the diagnostic tests available for lactose malabsorption
| Hydrogen breath test | Lactose tolerance test | Duodenal lactase activity | Serum gaxilose or urine galactose test | Genetic test | |
| Lactose challenge | Yes | Yes | No | Yes (gaxilose) | No |
| Assessment of symptoms and LI | Yes/possible | Yes/possible | No/not possible | No/not possible | No/not possible |
| Test principle | Detection of H2 in expiratory air | Increase in plasma glucose after lactose challenge | Lactase enzymatic activity in duodenal biopsy | Detection of D-xylose in serum or Galactose in urine after cleavage of orally administered 4-galactosylxylose (gaxilose) by lactase | Detection of −13910 C/T polymorphism |
| Detection of secondary LM | Yes | Yes | Yes | Yes | No |
| Costs | Low | Lowest | High (if costs for endoscopy are included) | Intermediate | High |
| Limitations | False-negative tests by H2-non- producer. False-positive tests with SIBO, rapid transit, altered bowel anatomy | Disorders of glucose metabolism, altered bowel anatomy | Patchy expression of lactase | Variable test performance in literature. False-positive tests with SIBO, rapid transit and other conditions | False negative in the presence of atypical mutations (relevant in non-Caucasian populations) |
| Best use | Test of choice to assess LM and symptoms (LI) | Low resource setting, LM epidemiology | If gastroscopy is performed for other reasons | To be determined | LD/LNP epidemiology |
LD, lactase deficiency; LI, lactose intolerance; LM, lactose malabsorption; LNP, lactase non-persistence; SIBO, small intestinal bacterial overgrowth.