LOWER VALUES FOR IMMUNOGLOBULIN-M IN CEREBROSPINAL-FLUID WHEN SAMPLEDWITH AN ATRAUMATIC SPROTTE NEEDLE COMPARED WITH CONVENTIONAL LUMBAR PUNCTURE

Immunoglobulin M (IgM) has a very low concentration in cerebrospinal f luid (CSF) compared with serum, and therefore determinations of IgM in CSF are highly sensitive to pre-analytical errors caused by contamina tion with serum or interstitial fluid. Capillary attraction causes a t hin layer of liquid containing serum proteins to be formed inside a co nventional (Quincke) needle during penetration of tissue. To investiga te this source of pre-analytical error, 35 patients had lumbar punctur es using a 22 G atraumatic (Sprotte) or 25 G conventional (Quincke) ne edle according to a randomized scheme, and the IgM concentrations in C SF and serum were determined. The CSF IgM concentrations for samples t aken with a Sprotte needle were significantly lower than those taken w ith a Quincke needle (P < 0.05), whereas the corresponding serum IgM c oncentrations and CSF erythrocyte counts did not differ significantly. The difference indicates that CSF IgM concentrations determined after conventional sampling may be falsely increased by contamination. We c onclude that IgM concentrations in CSF samples taken with the atraumat ic technique are more accurate, and recommend the use of this techniqu e when CSF IgM is to be determined.