A fecal pH test is one where a specimen of feces

Feces

Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...

 is tested for acidity in order to diagnose a medical condition. Human feces is normally alkaline. An acidic stool can indicate a digestive problem such as lactose intolerance

Lactose intolerance

Lactose intolerance, also called lactase deficiency or hypolactasia, is the inability to digest and metabolize lactose, a sugar found in milk...

 or a contagion such as E. coli

Escherichia coli

Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

 or Rotavirus

Rotavirus

Rotavirus is the most common cause of severe diarrhoea among infants and young children, and is one of several viruses that cause infections often called stomach flu, despite having no relation to influenza. It is a genus of double-stranded RNA virus in the family Reoviridae. By the age of five,...

.

Test procedure

The test is fast and can be performed in a doctor's office. A patient must not be receiving antibiotics. At least half a milliliter of feces is collected and a strip of nitrazine

Nitrazine

Nitrazine or phenaphthazine is a pH indicator dye.-Nitrazine test:As the disodium salt, it is used in pH testing strips for medical applications. It is also used in civil engineering to determine the carbonation spread in concrete structures and therefore assess the state of the rebar's...

paper is dipped in the sample and compared against a color scale. A pH of less than 5.5 indicates an acidic sample.