The CSF that is withdrawn during an LP is evaluated for color, blood, cells, bacteria, malignant cells, glucose, protein, chloride, lactic dehydrogenase, lactic acid, and glutamine. Normal findings for those evaluations (as well as pressure in the canal), and their possible significance, are as follows:

 

The Evaluation	Normal Findings	What abnormal findings may indicate
Pressure	Less than 200cm H2O	tumors, hydrocephalus, intracranial bleeding
Color	Clear and colorless	Cloudy-bacteria, WBCs Red-tinged--subarachnoid bleeding
Blood	None	Cerebral hemorrhage or Traumatic tap (inadvertant rupturing a blood vessel )
Cells	No Red blood cells, <5 lymphocytes/mm2	Red blood cells--an indication of the amount of blood within the spinal canal, White blood cells--cerebral abcess, bacterial meningitis, viral meningitis, tubercular meningitis, encephalitis
Culture & Sensitivity	No organisms present	Bacterial or fungal infection
Protein	15 - 45 mg/dl up to 70mg/dl for elderly and children	Meningitis, encephalitis, myelitis, tumors, inflammatory processes
Glucose	50 - 75 mg/dl or 60 to 70% of blood glucose level	Meningitis, neoplasm
Chloride (not routinely evaluated)	700 - 750 mg/dl	Meningeal infections, tubercular meningitis
Lactic dehydrogenase	<2.0 - 7.2 U/ml	Bacterial meningitis, inflammation
Lactic acid	10 - 25 mg/dl	Bacterial or fungal meningitis
Cytology	No malignant cells	Tumors of brain or spinal cord
Glutamine	6 - 15 mg/dl	Hepatic encephalopathy, Reye's syndrome

 

Advantages
The LP is an important diagnostic tool. It allows an inside look at the spinal cord's environment--which gives us a closer look at some brain functions too. It is a relatively easy procedure to perform--and fairly inexpensive. With an experienced doctor, the LP has a low percentage of complications. It may be done very quickly, and in almost any setting. 

Disadvantages/Possible Complications
There are some disadvantages and possible complications to doing an LP.

• Severe headaches caused by CSF leakage (spinal headache).
• Meningitis from introducing bacteria into the CSF.
• Back or leg pain/paresthesia.
• Accidental puncture of the spinal cord.
• Accidental puncture of the aorta or vena cava, causing serious hemorrhage.
• Herniation of the brain. In a patient with increased pressure, the sudden decrease of pressure through the LP, could cause herniation of the brain--compression of the brain stem.