If live bacteria are to be cultured, the LP
must be performed before or, if that is not possible,
immediately following the administration of
antibiotics. The introduction of molecular techniques
has, however, meant that live organisms
are not required for identification, so there is less
need for an early CSF. Blood polymerase chain
reaction (PCR) may be negative, whereas PCR
performed on CSF collected after treatment and
stabilisation can still be informative (see below
for further discussion of molecular techniques).