Body Fluids- Cerebrospinal Fluid

CSF

Clear fluid that circulates through ventricles and subarachnoid space

Primary functions of CSF

Nourishes CNS, removes metabolic waste, cushions brain and spinal cord

Normal CSF volume adult

140 to 170 milliliters

Normal CSF volume neonate

10 to 60 milliliters

Choroid plexus

Specialized capillary network that produces CSF

CSF circulation

Ventricles to subarachnoid space between arachnoid and pia mater

Blood brain barrier

Selective filtration barrier controlling passage from blood to CSF

Pleocytosis

Increased WBC count in CSF indicating inflammation

Indications for CSF analysis

Meningitis, multiple sclerosis, encephalitis, SAH, demyelinating disease

Lumbar puncture

Procedure to collect CSF via needle insertion

Lumbar puncture site

Between L4 and L5 vertebrae

CSF opening pressure

Reflects intracranial pressure at start of collection

Increased opening pressure

Seen in infection, hemorrhage, tumors

CSF closing pressure

Pressure measured after fluid removal

Normal CSF opening pressure

70 to 180 mm H2O

CSF tube 1

Hematology testing including cell counts

CSF tube 2

Chemistry and immunology testing

CSF tube 3

Microbiology testing including cultures and Gram stain

CSF tube 4

Additional hematology or special tests

Importance of tube order

Helps differentiate traumatic tap from true hemorrhage

Traumatic tap

Blood introduced during lumbar puncture

Traumatic tap finding

RBC count decreases in successive tubes

Non traumatic hemorrhage

RBC count remains constant across tubes

Xanthochromia

Yellow discoloration of CSF supernatant

Cause of xanthochromia

Hemoglobin breakdown from prior hemorrhage

Xanthochromia significance

Indicates preexisting bleed not procedural trauma

Normal CSF appearance

Clear and colorless

Cloudy CSF

Increased WBCs or microorganisms

Milky CSF

High lipid or WBC content

Bloody CSF

Hemorrhage or traumatic tap

Normal CSF WBC count

0 to 5 cells per microliter

Normal CSF RBC count

0 cells per microliter

Neutrophils in CSF

Suggest acute bacterial meningitis

Lymphocytes in CSF

Suggest viral, TB, or fungal meningitis

Monocytes in CSF

Seen in chronic inflammation

Macrophages with ingested RBCs

Indicate resolving hemorrhage

Plasma cells in CSF

Suggest chronic inflammation such as MS

Malignant cells in CSF

Indicate CNS malignancy or metastasis

CSF cell count timing

Must be performed within 1 hour of collection

Delayed CSF analysis

Causes cell degeneration and false low counts

Hemacytometer

Manual counting chamber used for CSF cell counts

Diluting fluid for CSF counts

Normal saline, not WBC diluting fluid

Normal CSF protein

15 to 45 milligrams per deciliter

Major CSF protein

Albumin

Prealbumin

Second most abundant CSF protein

Proteins absent in normal CSF

IgM, fibrinogen, beta lipoprotein

Decreased CSF protein

Seen in CSF leakage

Increased CSF protein

Seen in BBB damage, infection, hemorrhage, demyelination

CSF albumin index

CSF albumin divided by serum albumin

Normal albumin index

Less than 9 indicating intact BBB

Increased albumin index

Indicates BBB damage

CSF IgG index

Measures intrathecal IgG production

Elevated IgG index

Greater than 0

77 indicating CNS IgG synthesis

Oligoclonal bands

Discrete IgG bands present in CSF but not serum

Oligoclonal bands significance

Strongly associated with multiple sclerosis

Electrophoresis comparison

CSF and serum run simultaneously to exclude crossover

Normal CSF glucose

60 to 70 percent of serum glucose

CSF glucose testing requirement

CSF and blood glucose drawn simultaneously

Decreased CSF glucose

Seen in bacterial and TB meningitis

Normal CSF glucose with lymphocytosis

Suggests viral meningitis

CSF glycolysis

Occurs rapidly if testing delayed

CSF lactate

Marker for meningitis severity

Normal CSF lactate

Less than 25 milligrams per deciliter

Elevated CSF lactate

Seen in bacterial, TB, and fungal meningitis

CSF lactate in viral meningitis

Usually normal

False elevated CSF lactate

Seen in hemolyzed or xanthochromic specimens

CSF glutamine

Indirect indicator of ammonia levels

Normal CSF glutamine

8 to 18 milligrams per deciliter

Elevated CSF glutamine

Seen in liver disease and Reye syndrome

CSF glutamine significance

Correlates with altered consciousness

Myelin basic protein

Protein released during myelin breakdown

MBP elevation

Indicates active demyelination

MBP clinical use

Monitoring disease activity in multiple sclerosis

CSF microbiology

Used to identify causative organisms of meningitis

CSF Gram stain

Rapid presumptive test for bacterial meningitis

Acid fast stain CSF

Used for suspected tubercular meningitis

India ink preparation

Detects Cryptococcus neoformans capsule

Latex agglutination test

Rapid antigen detection for meningitis pathogens

Limulus lysate test

Detects endotoxin from gram negative bacteria

CSF VDRL

CDC recommended test for neurosyphilis

CSF VDRL limitation

Low sensitivity but high specificity

FTA ABS CSF

Highly sensitive treponemal test

Blood contamination in CSF serology

Causes false positive antibody results

CSF findings bacterial meningitis

High neutrophils, low glucose, high protein, high lactate

CSF findings viral meningitis

Lymphocytes, normal glucose, mild protein increase

CSF findings TB meningitis

Lymphocytes, very low glucose, high protein

CSF findings fungal meningitis

Lymphocytes, low glucose, elevated protein