Cerebrospinal fluid biochemical tests, including cerebrospinal fluid protein quantification, cerebrospinal fluid glucose quantification, and cerebrospinal fluid chloride quantification. Abnormal cerebrospinal fluid protein quantification is generally seen as an increase in the permeability of the blood-brain barrier. Cerebrospinal fluid glucose levels are approximately 60% of blood glucose, and elevation is seen in diabetes or after glucose solution injection. When a bacterial or fungal infection occurs in the central nervous system, the lesion releases glucolytic enzymes, which in turn consume glucose, causing the level of glucose in the cerebrospinal fluid to decrease. In the early stages of septic meningitis, the drop in glucose is very pronounced. In contrast, in tuberculous meningitis and novel cryptococcal meningitis, the glucose decline is mostly seen in the middle to late stages. In viral meningitis, the level of glucose is normal. The ratio of cerebrospinal fluid chloride levels to blood chloride levels was 1.25:1, whereas in tuberculous meningitis and septic meningitis, a decrease in cerebrospinal fluid chloride was seen, especially in tuberculous meningitis.