From the Guidelines
To diagnose lactose intolerance, the hydrogen breath test is the most recommended diagnostic tool, as suggested by the British Society of Gastroenterology in 2018 1. This test involves the patient consuming a lactose-containing beverage, and then their breath hydrogen levels are measured at intervals over 2-3 hours.
- Elevated hydrogen levels indicate undigested lactose being fermented by gut bacteria, which is a strong indicator of lactose intolerance.
- The lactose tolerance test, which measures blood glucose levels after consuming lactose, can also be used, but it is not as reliable as the hydrogen breath test, as stated in the 2003 guidelines for the investigation of chronic diarrhoea 2. Some other options for diagnosis include:
- Stool acidity tests, which can be useful for infants and children, as undigested lactose creates lactic acid and other acids in the stool.
- Genetic testing, which can identify lactase persistence/non-persistence genes, but does not always correlate perfectly with symptoms.
- A trial elimination diet, removing lactose for 2-4 weeks followed by reintroduction, can also help diagnose lactose intolerance based on symptom resolution and recurrence, as suggested in the 2018 guidelines 1. It is essential to note that a negative result from the hydrogen breath test does not exclude the diagnosis, and a trial of a lactose-free diet should be considered if the diagnosis is still suspected, as stated in the 2003 guidelines 2.
From the Research
Diagnostic Tests for Lactose Intolerance
To diagnose lactose intolerance, several tests can be ordered, including:
Lactose Hydrogen Breath Test
The LHBT measures the amount of hydrogen in the breath after consuming a lactose load. A positive test result is indicated by a persistent rise in breath hydrogen by 20 ppm 3.
- The test can be performed with different lactose loads, such as 50 g 3 or 25 g 4
- A lower lactose load of 12.5 g may also be used to evaluate the prevalence of lactose intolerance 4
Lactose Tolerance Test
The LTT measures the change in blood sugar levels after consuming a lactose load. A positive test result is indicated by a failure of blood sugar to rise by >20 mg/dL above basal level 3.
- The test is considered easy and efficient for diagnosing lactose malabsorption 3
- A positive LTT is associated with a higher breath hydrogen score than negative LTT 3
Comparison of Diagnostic Tests
- The LHBT and LTT have been compared in their ability to diagnose lactose malabsorption, with 125 (65%) and 137 (71%) patients testing positive for LHBT and LTT, respectively 3
- The 25 g lactose tolerance test may be substituted by the 12.5 g test in the diagnosis of lactose intolerance, as most patients with a positive 25 g test normally absorb a lower dose of lactose 4