Stool Acidity Test for Lactose Intolerance

Stool acidity testing is done to help diagnose lactose intolerance in infants and children.

Stool acidity testing is done to help diagnose lactose intolerance in infants and children.

Lactose is the sugar found in milk and milk products, including human breast milk. Lactose intolerance is the inability of the small intestine to digest lactose because of the lack of the lactase enzyme.

In normal digestion, lactose (lact=milk + ose=sugar) in the diet is digested into smaller sugars by lactase (lact=milk + ase=breakdown). These smaller sugars are absorbed into the body and used for energy. If lactase is not present, the lactose moves into the large intestine (colon) where normal bacteria ferment it into hydrogen gas and fatty acids.

The causes of lack of lactase in the small intestine include:

• Primary lactase deficiency – This is the most common type of deficiency and occurs as lactase levels gradually decrease with age. Symptoms often begin in teen years or early adulthood.
• Secondary lactase deficiency (lactose intolerance) – This occurs when the small intestine becomes inflamed from infection, celiac disease, or inflammatory bowel disease.
• Congenital lactase deficiency – this a rare genetic condition where the body does not make lactase. It is more prevalent in people of Asian, Native American, and some African (Nigerian and Bantu) descent.
• Developmental lactase deficiency – This occurs in premature infants whose small intestine has yet to develop the ability to produce lactase.

The symptoms of lactose intolerance include bloating, cramping, diarrhea, nausea, and vomiting. In infants and small children, the amount of diarrhea can cause dehydration, and the lack of sugar absorption may contribute to malnutrition.

The stool acidity test begins with feeding the infant or child a small amount of lactose. Stool is then collected from the diaper and sent to the laboratory for pH testing to determine the stool’s acidity. Just a small quantity of stool is required for testing, but it cannot be mixed with urine, because this will affect the test.

The test is positive if the stool pH is less than 5.5

Lactose hydrogen breath test

While stool acidity testing is the test of choice in infants and children, the lactose hydrogen breath test is preferred as the patient gets older.

In the hydrogen breath test, the patient is given lactose to drink, a face mask is placed, and the amount of hydrogen exhaled in the breath is measured over many minutes. The test is positive if the amount of hydrogen concentration in the breath increases.

Lactose tolerance test

A lactose tolerance test may also be considered to make the diagnosis. After the lactose is given, blood is drawn at 0, 60, and 120 minutes to measure blood sugar levels. The test is positive if the blood sugar level does not rise.

These tests require a significant lactose dose to be given, and in an infant with lactase deficiency, this may cause significant diarrhea leading to dehydration. There may be difficulty fitting a mask to collect the exhaled air, and the blood tests may not be tolerated well by an infant.

The stool acidity test is positive and consistent with lactose intolerance when the stool pH is less than 5.5

What is the normal pH of stool?

The normal pH of stool is 6.5-7.5.

Is acidic stool normal? What are other causes of high acidity in stool?

Acidic stool is not normal and its presence can confirm the diagnosis of lactose intolerance. Intestinal infection with E.coli and rotavirus can make the stool acidic, as can complications of Crohn’s disease, bile acid diarrhea and overgrowth of acid producing bacteria.