VCP 411: Medicine Section

ANALYTICAL METHODS

• Specific gravity is determined with a hygrometer and total white cell counts are performed using a haemocytometer. Smears of CSF are air dried within two hours of collection and stained with Leishman’s stain. The differential count should be based on a minimum of 20 cells. Serum albumin concentration is determined by the bromocresol green dye binding technique and protein fractionation by agarose gel electrophoresis. A postal delay of one to three days between CSF collection and analysis at the laboratory will not significantly influence the CSF protein concentration nor the total white cell concentration. Some deterioration of cell morphology will occur with this delay and render cell differentiation more difficult. Overall, however, the combination of CSF protein concentration and total white cell count will permit an accurate assessment of intrathecal inflammatory change.
• Typically, a cisternal sample is preferred if a brain lesion is suspected, eg, meningitis, and a lumbar sample in the case of a spinal lesion such as an epidural or vertebral body abscess. In fact, however, there is no significant difference between cisternal and lumbar samples for the majority of central nervous system lesions. (An exception would be a lesion compressing the spinal cord, such as an epidural or vertebral body abscess; stagnation of CSF caudal to the lesion results in a marked increase in the lumbar CSF protein concentration which is not present in the cisternal samples.)