All about CSF 

WBCs

- Normal WBC in adult is <5, in neonates < 20

- 99% of subjects with bacterial meningitis will have WBC > 100, 87% will have > 1000

- <100 = think viral meningitis 

- DDx for elevated WBC in CSF - seizure, ICH, tumor, inflammatory CNS dz 

- A traumatic tap will increase WBC in CSF at a ratio of 500-1000:1 (RBC to WBC). Correction factor can be applied to determine "true" WBC. Shortcut: if the RBC:WBC ratio in the CSF is <<500-1000:1, it's probably infected 

- Normal CSF: 70% lymphs, 30% monos 

Organisms (more relevant for standardized tests than for clinical practice) 

- Gram stain positive in 60-80% of untreated bacterial meningitis, 40-60% of partially treated

- Sensitivity of gram stain >90% for Staph and Strep, ~50% for listeria. 

- Sensitivity of india ink for cryptococcus ~50% 

- Sensitivity of first acid-fast stain ~33% for TB, increased to >85% if 4 smears are done 

- Dx toxo via giemsa or wright stain 

Protein 

- Newborn should be <150, adults~15-45 (varies by lab) 

- Can be elevated in bleeds, inflammatory disease (MS, GBS), tumors, infections/abscesses

- Can be falsely elevated in traumatic tap - to correct, subtract 1 mg/dL protein for every 1000 RBC

- Table of pathology: (from Fishman RA. Cerebrospinal fluid in diseases of the nervous system. 2d ed. Philadelphia: Saunders, 1992) 

 

	Average: mg per dL (g /L)	Range: mg per dL (g / L)
Bacterial meningitis	418 (4.18)	21 to 2220 (0.21 to 22.2)
Brain tumor	115 (1.15)	15 to 1920 (0.15 to 19.2)
Brain abscess	69 (0.69)	16 to 288 (0.16 to 2.88)
Aseptic meningitis	77 (0.77)	11 to 400 (0.11 to 4.0)
Multiple sclerosis	43 (0.43)	13 to 133 (0.13 to 1.33)
Cerebral hemorrhage	270 (2.7)	19 to 2110 (0.19 to 21.1)
Epilepsy	31 (0.31)	7 to 200 (0.07 to 2.0)
Acute ETOH	32 (0.32)	13 to 88 (0.13 to 0.88)
Neurosyphilis	68 (0.68)	15 to 4200 (0.15 to 42.0)

Glucose

- CSF glucose should be ~ 2/3 of serum glucose, although the ratio decreases as the serum glucoses increases; regardless of serum glucose, CSF glucose should almost always be <300 

- DDx decreased CSF glucose: infection, bleed, inflammation, hypoglycemia 

Viral Meningitis 

- >85% enteroviruses (echo, coxsackie) 

- Oral fecal or respiratory

- Affect people in the warmer months-  summer or early fall 

- Children < 3 mos = generally coxsackie B 

- Coxsackie B in pregnant women - harmless to mom, can cause serious cardiac infection to fetus in perinatal period 

CSF Color 

- CSF protein >150 or RBC>100,000 (traumatic tap) or serum bili > 10-15 can cause xanthochromia 

- Yellow: blood breakdown products, hyperbilirubinemia 

- Orange: blood breakdown pdts, excessive carotenoid ingestion 

- Pink: blood breakdown 

- Green: hyperbili, pus 

- Brown: meningeal melanomatosis 

- Xanthochromia can be seen as early as 2-4 hrs and will linger for weeks; in a suspected SAH, most people advise waiting 12 hrs after the suspected bleed to LP to give sufficient time for xanthochromia to develop 

- Neonates will often have xanthochromia in CSF 2/2 elevated bilirubin and protein