What is the purpose and procedure of a lactose tolerance test?

Lactose Tolerance Test: Purpose and Procedure

The hydrogen breath test is the most widely used and recommended method for diagnosing lactose intolerance, as it is non-invasive, relatively inexpensive, and has good sensitivity and specificity compared to other available tests. 1

Purpose of the Lactose Tolerance Test

• The lactose tolerance test aims to diagnose lactose malabsorption, which occurs when there is reduced expression or activity of lactase enzyme in the small intestine 2
• It helps identify patients who may benefit from dietary modifications, particularly those who regularly consume more than 0.5 pint (280 ml) of milk or equivalent dairy products daily 3
• The test distinguishes between true lactose intolerance and other conditions with similar symptoms, such as irritable bowel syndrome 1
• It's particularly useful in populations with high prevalence of lactase deficiency, which affects approximately 68% of the world's population and approaches 100% in some ethnic groups like the Han Chinese 3

Procedure of the Hydrogen Breath Test (Most Common Method)

• The patient fasts overnight before the test 1
• 25-50g of lactose dissolved in 200-500ml of water is ingested by the patient 3
• End-expiratory breath samples are collected at 15-30 minute intervals for three hours 3
• A rise in hydrogen concentration from baseline levels by more than 20 parts per million indicates a positive diagnosis 3
• Symptoms are monitored during the test, including abdominal pain, bloating, flatulence, and diarrhea 4

Alternative Testing Methods

• Lactose tolerance test measuring serum glucose or galactose in response to an oral lactose load 3
• Genetic testing for lactase non-persistence (particularly the 13 910 C/C genotype in Caucasian populations) 3
• Assay of mucosal lactase (more invasive as it requires biopsy) 3
• Blinded oral challenge with lactose and placebo (considered the gold standard by NIH) 4

Clinical Considerations and Limitations

• False negative rates can be as high as 25% with breath hydrogen testing, often due to hydrogen non-excretion 1
• A negative breath test does not exclude the diagnosis; a trial of lactose-free diet should still be considered if symptoms are suggestive 1
• Patient self-reports of lactose intolerance correlate poorly with objective evidence and cannot be relied upon 3
• Lactase deficiency should be regarded as normal in most non-Caucasian populations after age two 3
• Secondary causes of lactose intolerance should be considered, including celiac disease, gastroenteritis, non-steroidal anti-inflammatory drug use, and small bowel disease 1

Management Following Diagnosis

• If lactose intolerance is confirmed, the primary approach should be dietary modification with temporary reduction or removal of lactose from the diet 1
• Enzyme replacement therapy is an alternative option for those who wish to continue consuming dairy products 5
• Some patients may adapt to increased lactose consumption over time, with studies showing decreased hydrogen production after sustained dairy intake 6
• Probiotics and prebiotics may help improve lactose digestion in some patients 5