Cerebrospinal fluid CSF In adults approximately 500 m

Cerebrospinal fluid CSF

• In adults, approximately 500 m. L of cerebrospinal fluid (CSF) is produced each day (0. 3 -0. 4 m. L/min). • The total adult volume varies from 90 -150 m. L. • In neonates, the volume varies from 10 -60 m. L. • Thus, the total CSF volume is replaced every 5 -7 hours

The CSF has several major functions: • (a) it provides physical support since the 1500 g brain weighs about 50 g when suspended in CSF; • (b) it confers a protective effect against sudden changes in acute venous and arterial blood pressure or impact pressure; • (c) it provides an excretory waste function since the brain has no lymphatic system; • (d) it is the pathway whereby hypothalamus releasing factors are transported to the cells; • (e) it maintains central nervous system ionic homeostasis.

Specimen Collection • Cerebrospinal fluid may be obtained by lumbar puncture, or spinal tap. A spinal needle is inserted, usually between the 3 rd and 4 th lumbar vertebrae in the lower spine. Once the needle is properly positioned in the subarachnoid space (the space between the spinal cord and its covering, the meninges), pressures can be measured and fluid can be collected for testing.

• The CSF specimen is usually divided into three serially collected sterile tubes: • tube 1 for chemistry and immunology studies; • tube 2 for microbiologic examination; and • tube 3 for cell count and differential.

• Normal CSF is crystal clear and colorless and has a viscosity similar to that of water. • Abnormal CSF may appear cloudy, frankly purulent, or pigment tinged. • Turbidity or cloudiness begins to appear with leukocyte (WBC) counts over 200 cells/μL or red cell (RBC) counts of 400/μL.

• Appearance – If CSF is not crystal clear, a pathologic condition of the CNS should be suspected – Compare fluid to water – Fluid may be clear with as many as 400 RBCs/mm 3 and 200 WBCs/mm 3

• Cells – WBC counts over 5 cells/mm 3 should be taken to indicate the presence of pathologic condition – Polymorphonuclear leukocytes are never seen in normal adults – Neutrophilic pleocytosis is commonly associated with bacterial infections or early stages of viral infections, tuberculosis, meningitis, hematogenous meningitis, and chemical meningitis due to foreign bodies.

• Glucose – Low CSF glucose concentration indicates increased glucose use in the brain and the spinal cord. – The normal range of CSF glucose is between 50 and 80 mg/dl – 60 -70% of serum glucose concentration – Only low concentrations of glucose are significance

• Protein – Increase in CSF total protein levels are a nonspecific abnormality associated with many disease states. – Levels > 500 mg/dl are uncommon and are seen mainly in meningitis, in subarachnoid bleeding, and with spinal tumors.