Microscopic observation

A sample is taken from the site of a suspected infection, such as your throat, lungs, genitals, or a skin wound. Gram stains may also be used to check for bacteria in certain body fluids, such as blood or urine.

A Gram stain is most often used to find out if you have a bacterial infection. If you do, the test will show whether the bacteria in your infection is Gram-positive or Gram-negative. This may help your provider decide what other tests are needed to help identify which bacteria are causing your infection and how to treat it.