1. Cerebrospinal fluid
Definition; It is the water clear fluid surrounding the brain and spinal cord. Formation; The cerebrospinal fluid is formed as an ultra filtrate of the plasma by the choroid plexuses of the brain .The process is not one of simple filtration since active secretary processes are involved . Around ml of CSF is produced per day , but its total volume is ml only since it is continuously reabsorbed back to blood . Function of the CSF: 1- A major function of the CSF is to cushion the brain within its solid vault.(since the brain and the CSF have approximately the same specific gravity so the brain simply floats in the fluid) 2- It carries nutrients to the brain and spinal cord and removes waste products . 3-It is important to maintain a constant pressure inside the head and around the spinal cord. Physical characteristics; 1- Volume ml . 2-Color , clear and colourless. 3-pH = Specific gravity

3. Cerebrospinal fluid
Chemical composition; 1- Isosmotic, but concentrations of particular ions differ from that found in plasma (lower conc. of Na+,K+, Ca2+, HCO3- x higher conc. of Mg2+, Cl- the high Cl- compensates for the low anionic protein content of the CSF.) 2- Total protein conc. is ~200-fold lower than in plasma . 3-Metabolites: glucose (lower than in serum)60% that in plasma (50-80mg/dl) since it is the major source of energy to the brain thus it is consumed., it contains urea ,enzymes hormones. 4-number of white blood cells is usually very low ( necessitating a manual WBC count). 5- No RBC are normally found .

4. CSF Analysis
Cerebrospinal fluid (CSF) analysis is a set of laboratory tests that examine a sample of the fluid surrounding the brain and spinal cord. Routine examination of CSF includes visual observation of color and clarity and tests for glucose, protein, lactate, lactate dehydrogenase, red blood cell count, white blood cell count ….. .
Purpose of the analysis; To investigate certain conditions such as;
Infections such as meningitis or other bacterial ,viral or parasitic infection .
Inflammation or auto immune disorders such as multyple scelorisis.
Bleeding in the brain and spinal cord
Or metastatic tumors (e.g., leukemia) . ,
Lumbar puncture; Primary care physicians frequently perform lumbar puncture, because cerebrospinal fluid (CSF) is an invaluable diagnostic window to the central nervous system (CNS).
Description;
Lumbar puncture is performed by inserting the needle between the fourth and fifth lumbar vertabrae (L4-L5). This location is used because the spinal cord stops near L2, and a needle introduced below this level will miss the cord.

5. Lumbar puncture;

6. Lumbar puncture;

7. Lumbar puncture;
Risks; In some circumstances, a lumbar puncture to withdraw a small amount of CSF for analysis may lead to serious complications. Lumbar punctures should be performed only with extreme caution, and only if the benefits are thought to outweigh the risks. In people who have bleeding disorders, lumbar puncture can cause hemorrhage that can compress the spinal cord.

8. CSF Analysis Normal results
Gross appearance: Normal CSF is clear and colorless.
CSF opening pressure: 50–175 mm H 2 O.
Specific gravity: 1.006–1.009.
Glucose: 40–80 mg/dL.
Total protein: 15–45 mg/dL.
LD: 1/10 of serum level.
Lactate: less than 35 mg/dL.
Leukocytes (white blood cells): 0–5/microL (adults and children); up to 30/microL (newborns).
Differential: 60–80% lymphocytes; up to 30% monocytes and macrophages; other cells 2% or less. Monocytes and macrophages are somewhat higher in neonates.
Gram stain: negative.
Culture: sterile.
Syphilis serology: negative.
Red blood cell count: Normally, there are no red blood cells in the CSF unless the needle passes through a blood vessel on route to the CSF

9. CSF Analysis
Gross examination;Routine examination of CSF includes visual observation of color and clarity and tests for glucose, protein, lactate, lactate dehydrogenase, red blood cell count, white blood cell count with differential, .
GLUCOSE. CSF glucose is normally approximately two-thirds of the fasting plasma glucose. A glucose level below 40 mg/dL is significant and occurs in bacterial and fungal meningitis and in malignancy. glucose is consumed by leukocytes and tumor cells. It can be elevated in DM.
PROTEIN. Total protein levels in CSF are normally very low, and albumin makes up approximately two thirds of the total. High levels are seen in many conditions including bacterial and fungal meningitis where it rises to 500 mg/dl, multiple sclerosis, tumors, hemorrhage leads to a more moderate increase( mg/dl) ,( Increased level of τ-protein indicates the Alzheimer's disease).
LACTATE. The CSF lactate is used mainly to help differentiate bacterial and fungal meningitis, which cause increased lactate, from viral meningitis, which does not.
LACTATE DEHYDROGENASE. This enzyme is elevated in bacterial and fungal meningitis, malignancy, and subarachnoid hemorrhage.

10. CSF Analysis
WHITE BLOOD CELL (WBC) COUNT. The number of white blood cells in CSF is very low, usually necessitating a manual WBC count. An increase in WBCs may occur in many conditions including infection (viral, bacterial, fungal, and parasitic), allergy, leukemia, multiple sclerosis, hemorrhage,
RED BLOOD CELL (RBC) COUNT. While not normally found in CSF, RBCs will appear whenever bleeding has occurred. Red cells in CSF signal subarachnoid hemorrhage, stroke,
GRAM STAIN. The Gram stain is performed on a sediment of the CSF and is positive in at least 60% of cases of bacterial meningitis.
SYPHILIS SEROLOGY. This involves testing for antibodies that indicate neurosyphilis. SYPHILIS SEROLOGY.
A bright red colour of the CSF indicates recent hemorrhage .
Xanthochrmia(yellow colouration of the CSF which appears several days after hemorrhage thus indicating earliar hemorrhage .
Turbid CSF indicates pus or large content of WBC thus indicating infection.