The Diagnostic Significance of CSF Lactic Acid Levels in Meningitis
In the diagnosis of ABM, the CSF lactic acid levels are second only to the CSF Gram stain as a
rapid and reliable indicator of ABM. It has been said that the CSF lactic acid levels offer no
information that cannot be inferred from CSF glucose levels. This is not the case. The CSF glucose
levels and CSF lactic acid levels are inversely proportional to each other. As the CSF glucose
decreases, the CSF lactic acid increases. With successful treatment, the CSF lactic acid levels and
CSF glucose levels are the first to normalize. It takes days for the initial PMN predominance in the
CSF to become lymphocytic, and a lymphocytic pleocytosis may persist in the CSF for weeks after
clinical resolution of the patient’s bacterial meningitis. The CSF lactic acid level decreases more
rapidly and acutely than does the CSF glucose. For example, if a patient hasS. aureus, acute
bacterial endocarditis, and has seeded the CSF resulting in an early purulent meningitis, the CSF
lactic acid level will be elevated before the Gram stain is positive or the CSF glucose levels have
dropped. The CSF lactic acid test is invaluable in separating viral from bacterial meningitis as well
as for identifying patients with partially treated meningitis (1,30–32).
Table 11 Differential Diagnosis of CSF with a Negative Gram Stain
.Predominantly PMNs/decreased glucose
Partially treated bacterial meningitis
Listeria monocytogenes
HSV-1
Tuberculosis (early)
Syphilis (early)
Neurosarcoidosis
Parameningeal infection
Septic emboli (2 8 to ABE)
Amebic meningoencephalitis
N. fowleri
Syphilis (early)
Posterior fossa syndrome
.CSF lactic acid
<3 mmol/L
Aseptic “viral” meningitis
Parameningeal infections
3-6 mmol/L
Partially treated meningitis
RBCs
TB/fungal meningitis
6 mmol/L
Bacterial meningitis
.CSF protein
Elevated (any CNS infection/
inflammation)
Very highly elevated
Brain tumor
Brain abscess
TB (with subarachnoid block)
Demyelinating CNS disorders
Multiple sclerosis
.RBCs
Traumatic tap
Posterior fossa syndrome
CNS bleed/tumor
HSV-1
L. monocytogenes
Leptospirosis
TB meningitis
Naegleria fowlerimeningoencephalitis
.Predominantly lymphocytes/normal glucose
Partially treated bacterial meningitis
Neurosarcoidosis
Neuroborreliosis
HIV
Leptospirosis
RMSF
Viral meningitis
Bland emboli (2 8 to SBE)
Parameningeal infection
TB/fungal meningitis
Meningeal carcinomatosis
.Predominantly lymphocytes/decreased glucose
Partially treated bacterial meningitis
LCM
Enteroviral meningitis
L. monocytogenes
Mumps
Leptospirosis
TB/fungal meningitis
Neurosarcoidosis
Meningeal carcinomatosis
.CSF eosinophils
CNS vasculitis
NSAIDs
Coccidioidomycosis
Neurocysticercosis
Angiostrongyliasis
Gnathostomiasis
Paragonimiasis
Shistosomiasis
Toxocara canis/cati (VLM)
CNS lymphomas
VA/VP shunts
Interventional contrast materialsAbbreviations: CSF, cerebrospinal fluid; HSV, herpes simplex virus; CNS, central nervous system; ABE, acute
bacterial endocarditis; LCM, lymphocytic choriomeningitis; SBE, subacute endocarditis; PMNs, polymorphonu-
clear leukocytes; RMSF, Rocky Mountain spotted fever; VA, ventriculo-atrial; VP, ventriculo-peritoneal; NSAIDs,
nonsteroidal inflammatory drugs. VLM, visceral larva migrans
146 Cunha and Smith