Repeat lumbar puncture in the diagnosis of meningitis.

Meningitis may be difficult to diagnose. If it is suspected clinically and a first lumbar puncture is normal, a second cerebrospinal fluid (CSF) sample may be required within a few hours to confirm the diagnosis. A child is presented in whom CSF was normal 14 hours after the onset of illness, but who 14 hours later showed the characteristic changes of purulent meningitis. This case differs from those previously cited in the literature, in that the blood cultures taken at the time of the first lumbar puncture were also negative.