I was wondering, what methods are used to analyze stool for medical purposes. So how do you identify whether something is wrong with a person by analyzing the stool.
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There are many studies you can do with stool samples, all looking for different things.
Some studies just look at the properties of the stool, like its color, how hard it is or even the smell. These are just done using your senses. Different colors or smells can be indicators of different illnesses, for example, stool can be yellow if, for some reason, the patient isn’t absorbing fat correctly.
Sometimes you also measure chemical properties, like the pH level. I don’t know exactly how these are done in real labs. The normal pH of stool is around 6.5 to 7.5, any value different may indicate the presence of other substances in the sample like some carbohydrates or fats, and that can be due to many reasons.
Another type of study is looking for blood in the stool, which indicates that the patient is bleeding somewhere within their GI tract. Blood indicates that there might be ulcers, hemorrhoids, tears in the colon or even cancer.
Other types of studies look specifically for things that shouldn’t be in stool, like high levels of white blood cells (high levels of WBC indicate an infection along the GI tract), fat (some parasites or conditions make it hard to absorb fat, so a lot of it ends up in the stool when it wasn’t supposed to), enzymes or other chemical compounds.
All those studies can give you a clue as to what kind of illness a patient could have, but the final diagnosis still depends on other symptoms, clinical history and other lab tests.
Some other tests, like looking for parasites or bacteria can be used to diagnose infections.
Looking for parasites is quite simple. Some parasites can be seen in the stool with the naked eye, while some others require the use of a microscope. There are other ways that can help you identify parasites indirectly, like inmuno assays (they look for proteins or antibodies within the stool) or PCR (the same that we use for some covid tests, it uses an enzyme to look for a specific sequence of DNA and copy it a lot).
Lastly, they can grow bacteria from the stool sample. To do that they take a tiny bit of stool and put it in a culture media, then they put it in a warm incubator and wait. After a couple of days they take the culture out of the incubator and see what grew. Since we have a good idea of what kinds of bacteria are present in the gut and intestines normally, we can tell when there are anomalies (bacteria that shouldn’t be there) and then proceed to identify them.
Hope this helps and I’d love to answer any further questions you have.
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