The indications for lumbar puncture include (common uses in bold):

• Diagnosis of central nervous system (CNS) infection
• Diagnosis of subarachnoid hemorrhage (SAH)
• Infusion of anesthetic, chemotherapy, or contrast agents into the spinal canal
• Treatment of idiopathic intracranial hypertension
• Evaluation and diagnosis of demyelinating or inflammatory CNS processes

Perhaps the most common indication for LP is to evaluate the patient for CNS infection. CSF samples are needed for the diagnosis of bacterial and viral meningitis as well as for numerous other infective processes such as CNS syphilis and other encephalopathies. The CSF may be examined for signs of infection by studying it for microbes, cells and culturing the CSF for organisms.

The diagnosis of subarachnoid hemorrhage is the other emergent indication for LP. In SAH, blood seeps into the CSF and can be detected by lumbar puncture. In this day and age, CT scan is often used to diagnose SAH, but LP is used when a CT scan may have missed the diagnosis of SAH. CT scan may miss small bleeds or bleeds which occurred greater than twelve hours prior to CT scan. In these instances, LP proves to be instrumental in the diagnosis or exclusion of SAH.

Other common indications for LP include spinal anesthesia for procedures and operations as well as injection for contrast agents into the spinal column for imaging such as in CT – myelography. CNS chemotherapy is often delivered after lumbar puncture. Other uses of LP include evaluation of inflammatory CNS processes such as multiple sclerosis.