The Gram stain test is a laboratory procedure used to identify and classify bacteria based on their cell wall structure. The test uses crystal violet dye, which is taken up by the cell walls of some bacteria, while others do not take it up.
Pre-test preparation: No special preparation is needed for the Gram stain test.
Testing method: A sample of bacteria is collected, usually from a patient’s infection site, and is placed on a microscope slide. Crystal violet dye is added to the sample, and then a decolorizing agent, such as alcohol or acetone, is applied. The slide is then rinsed with a counterstain, such as safranin, which stains any bacteria that did not take up the crystal violet dye. The slide is then examined under a microscope to identify and classify the bacteria.
Common symptoms for prescribing this test: This test is commonly used to diagnose bacterial infections such as strep throat, pneumonia, and urinary tract infections. It is also used to identify bacteria that are resistant to certain antibiotics.
Diagnosis: Based on the shape, size and color of the bacteria, the lab technician can determine if the bacteria are gram-positive or gram-negative. The gram-positive bacteria will appear purple, while the gram-negative bacteria will appear red.
Reference range: Not applicable
Gram-positive bacteria: Purple
Gram-negative bacteria: Red
It is important to note that the Gram stain test is only a preliminary test and should be used in conjunction with other diagnostic tests to confirm a bacterial infection. Also, the results of the test should be considered along with the patient’s clinical presentation and other laboratory test results to arrive at an accurate diagnosis.