you are here:

Lactose intolerance can be simply diagnosed by means of a non-invasive test, the hydrogen breath test, which measures the H2 concentration in expired air after oral administration of a dose of lactose.

The increase in H2 is a measure of the fermentation of non-absorbed lactose by the bacteria in the colon (1).

Other diagnostic methods, the lactose tolerance test, include measurement of the blood glucose level after the oral administration of lactose and the determination of lactase activity in a biopsy sample from the small intestine.

There are also similar tests available, which use isotope biomarkers measuring the exhaled marked CO2 present. Low levels indicate poor lactose digestion. Although these tests are able to prove if a lactase deficiency exists, they are unable to show what the cause is.

There is now a genetic test for lactose sensitivity, but this is not yet freely available (2). This test analyses a polymorphism at C/T13910 (3). A CC pattern at this locus in a white northern European always leads to lactose sensitivity. A 50g lactose challenge followed by breath analysis for hydrogen and methane, combined with symptom recording and dietary lactose exclusion, should be done on all suspected cases who are not ‘CC’. It is important to realize that some people produce symptoms within a few hours of ingesting lactose, while in others it may take 24-48h to suffer certain symptoms.

References

  1. Sahi T. Hypolactasia and lactase persistence. Historical review and the terminology Scand J Gastroenterol Suppl.1994; 202: 1-6.

  2. Jonathan P. Waud, JP, Matthews, SB and Campbell, AK. Measurement of Breath Hydrogen and Methane, together with Lactase Genotype, Defines the Current Best Practice for Investigation of Lactose Sensitivity. Annals Clin. Biochem. 2008 Jan;45:50-58.

  3. Enattah, NS, Sahi, T, Savilahti, E et al. Identification of a variant associated with adult-type hypolactasia. Nature Genetics 2002;30:233-237.