A sample of CSF is needed. This is usually done with a lumbar puncture (also known as a spinal tap).

The sample is sent to the laboratory. There, it is placed in a dish that has a special substance called a culture medium. Laboratory staff then observe if bacteria, fungi, or viruses grow in the dish. Growth means there is an infection.

Follow instructions on how to prepare for a spinal tap.

Your health care provider may order this test if you have signs of an infection that affects the brain or nervous system. The test helps identify what is causing the infection. This will help your provider decide on the best treatment.

A normal result means no bacteria, viruses, or fungi grew in the laboratory dish. This is called a negative result. However, a normal result doesn't mean that an infection is present. The spinal tap and CSF smear may need to be done again.

Bacteria or other germs found in the sample may be a sign of meningitis. This is an infection of the membranes covering the brain and spinal cord. The infection can be caused by bacteria, fungi, or viruses.

A laboratory culture poses no risk to you. Your provider will tell you about the risks of a spinal tap.

Culture - CSF; Spinal fluid culture; CSF culture

Karcher DS, McPherson RA. Cerebrospinal, synovial, serous body fluids, and alternative specimens. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 30.

O'Connell TX. Cerebrospinal fluid evaluation. In: O'Connell TX, ed. Instant Work-Ups: A Clinical Guide to Medicine. 2nd ed. Philadelphia, PA: Elsevier; 2017:chap 9.

Updated by: Jatin M. Vyas, MD, PhD, Associate Professor in Medicine, Harvard Medical School; Associate in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital, Boston, MA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.