Testing for Lactose Intolerance
Yes, lactose intolerance can be definitively tested using the hydrogen breath test, which is the most widely used and recommended diagnostic method. 1, 2
Primary Diagnostic Test: Hydrogen Breath Test
The hydrogen breath test is non-invasive, relatively inexpensive, and has good sensitivity and specificity compared to other available tests. 1, 3 Here's how it works:
- Patient ingests 25-50g of lactose dissolved in 200-500ml water after an overnight fast 4, 1
- Breath samples are collected at 15-30 minute intervals for three hours 4, 1
- A positive result is defined as a rise in hydrogen concentration from baseline by more than 20 parts per million 4, 1
Important Caveats About the Hydrogen Breath Test
The test has a false-negative rate of up to 25%, often due to hydrogen non-excretion which occurs in approximately 18% of tested subjects. 1, 2 This means a negative test does not exclude the diagnosis, and you should still consider a trial of a lactose-free diet if symptoms are suggestive. 4, 1
Alternative Diagnostic Approach: Dietary Restriction Trial
A simpler and more economical approach is a 2-week dietary restriction trial with symptom resolution as the diagnostic indicator. 1, 2 This can be particularly useful when:
- The hydrogen breath test is unavailable
- The breath test is negative but clinical suspicion remains high
- You want to confirm clinical relevance of a positive breath test
Other Available Tests (Less Commonly Used)
While other methods exist, they are generally used as supplementary tests rather than first-line diagnostics:
- Mucosal lactase assay on duodenal biopsies (invasive, requires endoscopy) 4
- Lactose tolerance test measuring serum glucose or galactose response 4
- Genetic testing for lactase persistence 3
- Quick lactase test on duodenal biopsies 5
The lactose quick test on duodenal biopsies may actually be more accurate than the breath test in predicting clinical response to a lactose-free diet (98% vs 81%), but requires endoscopy. 5
Who Should Be Tested?
Testing should be reserved for patients who regularly consume more than 0.5 pint (280 ml) of milk or equivalent dairy products daily. 1 Those consuming less than this amount can generally tolerate moderate quantities even if lactose intolerant. 1
Critical Pitfall to Avoid
Patient self-reports of lactose intolerance correlate poorly with objective evidence and cannot be relied upon. 1, 2 Don't accept self-diagnosis—objective testing or systematic dietary elimination is essential. 1
Before Testing: Rule Out Secondary Causes
Always consider secondary causes of lactose intolerance that may be reversible: 1, 2
- Celiac disease (must be excluded first) 1
- Gastroenteritis 4, 1
- NSAID use 4, 1
- Small bowel disease 4, 1
- Chemotherapy (causes reversible lactose intolerance in up to 35% of patients) 1
Consider Broader Differential
At least 50% of patients with presumed lactose intolerance actually have broader intolerance to FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols). 1 If lactose restriction alone doesn't resolve symptoms, implement a low FODMAP diet trial. 1