Table 4.

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.