Overview
CSF examination part three deals with the chemical analysis of cerebrospinal fluid, focusing on glucose, proteins, lactate, and enzymes such as LDH, ADA, CK, and GGT. These biochemical parameters provide crucial information about metabolic activity, integrity of the blood–brain barrier, and presence of infection, inflammation, hemorrhage, or malignancy in the central nervous system.
Normal CSF glucose is 45–80 mg/dl and is approximately 60 percent of blood glucose. CSF proteins normally range from 15–45 mg/dl and represent about 1 percent of plasma proteins. Lactate and enzyme levels further help in differentiating bacterial, viral, tuberculous, and fungal infections, as well as assessing tissue damage and prognosis.
Symptoms
Abnormal CSF biochemical findings are associated with neurological and systemic symptoms. Reduced CSF glucose and raised proteins are commonly seen in patients with fever, headache, neck stiffness, altered sensorium, and seizures suggestive of meningitis.
Elevated lactate levels may be associated with severe infection, hypoxia, or poor neurological outcome, presenting with worsening consciousness or signs of raised intracranial pressure. Enzyme elevation may correlate with neurological deficits, persistent symptoms, or poor recovery following brain injury. In some cases, biochemical abnormalities are detected even when clinical symptoms are subtle or evolving.
Causes
Decreased CSF glucose is caused by acute bacterial meningitis, tuberculous meningitis, fungal meningitis, meningeal carcinomatosis, and systemic hypoglycemia, while it remains normal in viral meningitis. Raised CSF protein occurs due to meningitis, spinal cord tumors, multiple sclerosis, neurosyphilis, Guillain–Barré syndrome, subacute sclerosing panencephalitis, traumatic tap, and subarachnoid hemorrhage.
Increased CSF lactate is due to anaerobic metabolism from tissue hypoxia and is markedly elevated in bacterial meningitis, moderately increased in viral meningitis, and associated with poor prognosis in severe head injury. Elevated ADA levels above 15 U/L suggest tuberculous meningitis. Increased LDH indicates CNS tissue damage and is seen in bacterial meningitis, intracranial hemorrhage, metastatic carcinoma, leukemia, and lymphoma. Changes in LDH isoenzymes add specificity in metastatic brain tumors and hypoxic brain injury.
Risk Factors
Risk factors for abnormal CSF chemical findings include central nervous system infections, tuberculosis, malignancy, head injury, hypoxic events, autoimmune disorders, and chronic inflammatory diseases. Newborns have different normal ranges for lactate and enzymes, increasing the risk of misinterpretation if age is not considered. Delay in processing CSF samples can falsely lower glucose levels due to glycolysis. Blood contamination during lumbar puncture may falsely elevate protein and enzyme levels.
Prevention
Prevention focuses on proper sample collection, handling, and prompt processing of CSF. Drawing a simultaneous blood glucose sample before lumbar puncture ensures accurate interpretation of CSF glucose. Immediate processing of CSF prevents false biochemical changes. Early diagnosis and timely treatment of infections, especially bacterial and tuberculous meningitis, help prevent severe biochemical derangements and neurological damage. Regular monitoring of CSF biochemical parameters aids in assessing treatment response and prognosis in central nervous system disorders.
