Lumbar puncture and CSF analysis and interpretation

Abstract

Cerebrospinal fluid (CSF) analysis is essential in the diagnosis of the infectious diseases of the central nervous system. It is also helpful in the differential diagnosis of other conditions that simulate infectious disorders and in monitoring the effects of antibiotic therapy. The CSF is formed by the choroid plexuses of the ventricles. Its volume in adults is 150 ml. Most of the CSF is reabsorbed by the arachnoid granulations, located along the superior sagittal sinus toward the venous system. The main CSF function is mechanical, protecting the brain from acute or sudden changes in pressure. The lumbar puncture (LP) to obtain CSF is not without risks, and the complications, such as brain herniation, spinal hematoma, and iatrogenic CNS infection, which, although rare, can be serious. Nevertheless, LP remains the gold standard procedure for the diagnosis of CNS infections. The LP should be performed in aseptic conditions with the patient assuming a lateral recumbent position. Local anesthesia at the needle insertion point makes the procedure easier. Using atraumatic needle is associated with less post-puncture headache, which is the commonest complication. The normal CSF appears sparkling clear; any change in this characteristic is pathologic. The normal total CSF leukocyte counts are <5/mm3 in adults, the normal glucose level is between 45 and 80 mg/dl, and the normal total protein is between 15 and 50 mg/dl. An increased intrathecal synthesis of immunoglobulins indicates a chronic infection of the CSF. Microbiological analysis of the CSF includes stains; aerobic and anaerobic cultures for bacteria, fungi, virus, and tuberculosis; serologic testing; and viral and bacterial screen by PCR.