gram-stain
Reviewed
A Gram stain is a test that checks for a bacterial infection. A sample from the suspected infection site is stained purple, then a solvent is added. Bacteria that stay purple are Gram-positive; bacteria that turn pink or red are Gram-negative. The test helps identify the type of infection and guide antibiotic choice.
Preparation and collection
You don't need any special preparations for a Gram stain.
Understanding this test
Use the reference interval and units printed by the laboratory that performed the test. A result outside that interval is not a diagnosis by itself, and a result inside it does not rule out every condition. Your symptoms, history, medicines, timing, and related tests can change what the result means.
- A Gram stain cannot detect a virus.
- Results may not identify the exact type of bacteria; a bacteria culture may be needed to confirm.
- If no bacteria are found, it may mean there weren't enough bacteria in the sample.
What to do next
If you are diagnosed with a bacterial infection, you will probably be prescribed antibiotics. It's important to take your medicine as prescribed, even if your symptoms are mild. This can prevent your infection from getting worse and causing serious complications. If you have questions about your results, talk to your provider.