Lactose tolerance test may be helpful in the diagnosis of lactose intolerance. Findings suggestive of lactose intolerance include bloating, diarrhea and abdominal pain and rising of blood glucose by less than 20 mg/dL after the ingestion of lactose. Genetic test can also be used for diagnosis of primary lactase deficiency that is associated with CC genotype at -13.9 kb upstream of the lactase gene.

Other diagnostic studies for lactose intolerance include:

• Lactose tolerance test^[1]
• Genetic test for primary lactase deficiency ^[2]

• 50 g of oral lactose in adults (2 g/kg in children) is administered and blood glucose levels are checked at 0, 60, and 120 minutes after the ingestion.
  • Symptoms such as bloating, diarrhea and abdominal pain and rising of blood glucose by less than 20 mg/dL (1.1 mmol/L) are diagnostic for lactose intolerance.
  • This test is used less than lactose breath hydrogen test because it needs repeated measurements of blood glucose level
•  False negative results cab be obtained due to
  • Diabetes
  • Bacterial overgrowth

• Acquired primary lactase deficiency is associated with a CC genotype at -13.9 kb upstream of the lactase gene and lactase persistence is related to TT genotype.^[2]