Lactose Tolerance Test


After weaning, most humans lose most of their lactase, the enzyme that cleaves lactose into galactose and glucose. Therefore, it is important to distinguish between hypolactasia, low level of lactase, and clinical lactose intolerance. Lactose intolerance causes gut pain and a range of systemic symptoms, though the threshold for lactose varies considerably between ethnic groups and individuals within a group. Lactose intolerance is defined as gut pain and distension, borborygmi, flatus, and diarrhoea induced by lactose. Other symptoms include nausea, vomiting, constipation, headaches, muscle and joint pain, various allergies, heart arrhythmia and others. The symptoms of lactose intolerance are caused by gases and toxins produced by anaerobic bacteria in the large intestine.


This test is used as an an aid in the diagnosis of lactose intolerance. The patient is given lactose orally and serial blood samples are taken at set time intervals and tested for glucose levels. In case of low or diminished lactase activity, little or no lactose in converted into glucose, thus, little or no rise in glucose level is detected.

Sample Type, Quantity & Conditions

1 ml Serum Each Room Temperature

Special Precautions

Fasting patient should be given 30g lactose in 200-300 mL water consumed in 5 min. Note: if severe lactose deficiency is suspected, the dose should be lowered.

Normal Range

Lactose Intolerance: Elevation in glucose level after lactose intake of < 25 mg/dL (<1.38 μmol/L) as compared to the fasting level.

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