Understanding Lab Values
Cultures can be done from many sources: blood, urine, pus, skin, nail, stool, and throat swab. Cultures are performed to identify a treatable source of fever and other symptoms, or to choose the best treatment for a known infection.
Cultures can grow bacteria, viruses, parasites, and fungus, depending on how they are treated. Identification of specific organisms is especially important as we see more "smart" bacteria that are not killed by most antibiotics.
After the sample is taken, it is stored in a way that encourages bacterial growth. In other words, if bacteria are in the sample, they are fed and cultured to grow so they can be tested and identified. Identification of a bacteria allows further testing to see what antibiotics will kill the bacteria. This testing usually requires an additional 24 hours after the bacteria is isolated. In general blood and wound (pus) cultures grow within 2-3 days, but are not final until 7 days. Urine cultures are finalized in 2-3 days. Throat cultures are finalized in 2-3 days. Often several stool samples collected over many days are required for adequate stool sampling.
Fungal cultures are occasionally done to identify if a fungus is causing an infection. They take up to 4 weeks to finalize. Virus cultures can be done, but other tests for viruses are often more practical (such as rapid influenza test or RSV test).