Abstract
Immunoglobulin M (IgM) has a very low concentration in cerebrospinal fluid (CSF) compared with serum, and therefore determinations of IgM in CSF are highly sensitive to pre-analytical errors caused by contamination with serum or interstitial fluid. Capillary attraction causes a thin layer of liquid containing serum proteins to be formed inside a conventional (Quincke) needle during penetration of tissue. To investigate this source of pre-analytical error, 35 patients had lumbar punctures using a 22 G atraumatic (Sprotte) or 25 G conventional (Quincke) needle according to a randomized scheme, and the IgM concentrations in CSF and serum were determined.
The CSF IgM concentrations for samples taken with a Sprotte needle were significantly lower than those taken with a Quincke needle (P < 0·05), whereas the corresponding serum IgM concentrations 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 conclude that IgM concentrations in CSF samples taken with the atraumatic technique are more accurate, and recommend the use of this technique when CSF IgM is to be determined.