Biochemical Investigations of Cerebrospinal Fluid Flashcards
Functions of CSF
- A shock absorber
- A mechanical buffer
- Acts as a cushion between the brain and cranium
- Acts as a reservoir and regulates the contents of the cranium
- Serves as a medium for nutritional exchange in CNS
- Transports hormones and hormone-releasing factors
- Removes metabolic waste products through absorption
Discuss circulation of CSF
CSF is mainly formed in choroid plexus of the lateral ventricle. CSF passes from the lateral ventricle to the third ventricle
through the interventricular foramen (foramen of Monro).
From third ventricle it passes to the fourth ventricle through the cerebral aqueduct. The circulation is aided by the arterial
pulsations of the choroid plexus
From the fourth ventricle (CSF) passes to the subarachnoid space around the brain and spinal cord through the foramen
of magendie and foramina of luschka.
How much CSF is produced per day?
20 ml/hour or 500ml/day
What are the layers that must be penetrated in administration of a lumbar puncture?
Skin, supraspinous ligaments, interspinous ligaments, ligamentum flavum epidural space, dura, subarachnoid membrane into subarachnoid space
How is CSF specimen collected?
Obtained by lumbar puncture (At the
interspace L3-4, or lower)
• Using aseptic technique
• CSF is separated into 3 aliquots:
for chemistry & serology for microbioloy for cell count
• Immediate analysis
• It’s a precious sample
What must be considered in CSF specimen collection
• Before analysis, fluid should be centrifuge to avoid contamination, cellular elements
• CSF is the most precious biological material
• Often, only small volumes of CSF are available for analysis due to difficulty in collection; hence handle this with care.
• Specimen may contain virulent organisms
so strict safety precautions should be followed
CONTRAINDICATIONS FOR PERFORMING
LUMBAR PUNCTURE:
1 . Bleeding disorders
2 . I n c r e a s e d i n t r a c r a n i a l
p r e s s u r e
3 . I n f e c t i o n a t s i t e o f n e e d l e
i n s e r t i o n
INDICATIONS FOR LABORATORY
INVESTIGATION OF C S F
1 . C N S infection
2 . Demyelinating diseases
3 CNS Malignancy
4 . Hemorrhage in C N S
P H Y S I C A L EXAMINATION of CSF
• N o r m a l C S F is:
C o l o r l e s s
C l e a r
• F r e e o f c l o t s
• F r e e o f b l o o d
• I f C S F is c l o u d y ( t u r b i d ) → p e r f o r m
m i c r o s c o p i c e x a m i n a t i o n :
• is u s u a l l y due t o leucocytes
• m a y b e d u e t o m i c r o - o r g a n i s m s
BLOOD & HEMOGLOBIN PIGMENTS IN
C S F could be due to
T r a u m a t i c t a p
• → bright red color
→ RBCS in decreasing
number as the fluid is
sampled
Subarachnoid hemorrhage
(SAH)
→ X a n t h o c h r o m i a
(hemoglobin breakdown
pigments) = RBCs lysis &
metabolism previously
occurred (at least 2 hr
e a r l i e r )
W H E N WOULD XANTHOCHROMIA INDICATE HEMORRHAGE?
• If you exclude:
1 . Prior traumatic tap
2 . Hyperbilirubinemia (bilirubin > 20 mg/dL)
BIOCHEMICAL ANALYSIS OF C S F
• Tests of interest:
G l u c o s e
• Protein
• Total
V Specific:
A l b u m i n
Immunoglobulin
Others (e.g. myelin basic protein; MBP)
The m o s t reliable
diagnostically &
accessible analytic
G L U C O S E IN C S F
• Gle enters C S via facilitative transporter (GLUT)
• CSF [glucose] is ~ 2/3 that of plasma
• 50 - 80 m g / d l
• A plasma sample must be obtained ~ 2-4 hr before CSF
sample
• In hypoglycemia: [CSF glucose] may be very low
• In hyperglycemia: [CSF glucose] is raised.
• Measure CSF [Glucose]:
i m m e d i a t e l y
ABNORMAL CSF [GLUCOSE]
• I C S F [glucose]:
1. Disorder in carrier-mediated transport
De.g. TB meningitis, sarcoidosis
2. Active metabolism of glucose by cells or organisms:
Oe.g. acute infection, amebic, & fungal meningitis
3. Increased metabolism by the CNS
Oe.g. by CNS neoplasm
• In viral meningitis CSF [glucose] is usually normal
PROTEIN IN C S F
• Proteins, mostly albumin are found in the
CSF (0.15-0.45 g/L)
• Source of CSF proteins:
• 80% from plasma by ultrafiltration
• 20% from local synthesis
