What does a lumbar puncture actually help to prove?

Depends: The most common indications are severe headaches or fever/neck pain. Lps will check for the presence of blood cells in the fluid (there is typically none). The presence of blood dells may indicate infection or bleeding as a cause of the symptoms above.

Spinal fluid answers: The question: does the patient have intracranial bleeding? (presence red cells or xanthochromia) or infection present? (presence of white cells, bacteria, viral culture/antigens) or multiple sclerosis (presence of abnormal proteins). Also a l.P. (lumbar puncture) may show a high opening pressure which is a sign of pseudo-tumor (cause of chronic headaches). L.P. 's are safer now done under xray.