Biochemical analysis of the liquor

The ratio of the number of cellular elements and protein is of significant importance for diagnostics.

Determination of the amount of protein in liquor

Normally, the cerebrospinal fluid contains 0.1-0.3 g/l of protein, mainly albumin. In neuroinfections and other pathological processes, the amount of protein increases with increased permeability of the hematocerebrospinal fluid barrier due to its entry from the blood plasma. In viral neuroinfections, the protein content can reach 0.6-1.5 g/l, in bacterial infections - 3.0-6.0 g/l, and in later stages - up to 16-20 g/l. The composition of proteins changes. In bacterial meningitis, globulins and even fibrinogen appear in the cerebrospinal fluid. In tuberculous meningitis, after the cerebrospinal fluid has been left to stand in the refrigerator for 24 hours, a network of thin fibrin threads appears in it, and in pneumococcal meningitis, a dense fibrin clot is formed.

In viral meningitis, in the early stages of bacterial meningitis, a sharp increase in the number of cells is observed with a normal protein content - cell-protein dissociation. In viral encephalitis, tumors, subarachnoid hemorrhage, a significant increase in protein concentration is possible with normal cytosis or minor pleocytosis - protein-cell dissociation.

The concentration of protein in the cerebrospinal fluid increases with a violation of the BBB, slow reabsorption or increased local synthesis of immunoglobulins (Ig). Violation of the BBB can occur due to inflammation, ischemia, trauma or tumor neovascularization. The normal concentration of protein in the lumbar cistern does not exceed 0.45 g / l and is the highest compared to that in other parts of the subarachnoid space. The protein content in the cerebrospinal fluid increases proportionally to the distance from the site of its synthesis and is up to 0.1 g / l in the ventricles of the brain, up to 0.3 g / l in the basal cistern of the brain, and up to 0.45 g / l in the lumbar cistern.

A significant increase in protein content is characteristic of Guillain-Barré syndrome (from the 3rd week of the disease) and CIDP. A particularly high protein concentration is typical for spinal cord tumors. Tumors of the lower parts of the spinal canal are often accompanied by the cerebrospinal fluid syndrome Froelich Nonne: the cerebrospinal fluid is xanthochromic, coagulates in a test tube upon flowing out, and the protein content in it is increased by 10-20 times.

Electrophoresis and immunoelectrophoresis are used for qualitative and quantitative analysis of cerebrospinal fluid proteins. Normally, about 70% is albumin and about 12% is y-globulins. Proteins in the cerebrospinal fluid come from the blood plasma by selective transport or are synthesized in the subarachnoid space itself. Therefore, an increase in the protein concentration in the fluid can occur both as a result of a general violation of the immunological status in the body and as a result of increased local synthesis. An increase in the concentration of y-globulins (hypergammaglobulinrachia) with a normal content of total protein is characteristic primarily of multiple sclerosis. If an increase in immunoglobulins is detected in the cerebrospinal fluid, then their level in the blood serum must be checked. An increase in Ig can also be observed with a normal content of total protein in the fluid. Thus, an increase in IgG is detected in multiple sclerosis and acute polyradiculoneuropathy, and sometimes in intracranial tumors and various inflammatory diseases of the central nervous system, including encephalitis, meningitis, subacute sclerosing panencephalitis, etc.

Polyclonal Ig form a single diffuse band during electrophoresis. Monoclonal Ig form separate distinct bands in the area of γ-globulin deposition. Since it is believed that each clone of B-lymphocytes produces specific Ig, a group of distinct bands (oligoclonal bands) that appear during electrophoresis reflects the presence of oligoclonal Ig synthesized by certain clones of lymphocytes in the cerebrospinal fluid. The fact that Ig is synthesized specifically within the CNS is confirmed by the absence of oligoclonal bands during electrophoresis of blood serum. Detection of oligoclonal bands is very important for the diagnosis of multiple sclerosis, since 70% of patients with a clinically reliable diagnosis of multiple sclerosis have oligoclonal bands during electrophoresis of the cerebrospinal fluid.

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Determination of the amount of glucose in the liquor

The hematoliquor barrier is semipermeable for glucose, so its content in the cerebrospinal fluid is on average 50% of the content in the blood and is within 2.2-3.3 mmol / l. Due to the increased permeability of the hematoliquor barrier in aseptic inflammatory processes, the amount of glucose increases to 3.5-5.0 mmol / l, and in viral serous meningitis and encephalitis it remains within 2.5-4.5 mmol / l. In bacterial meningitis, the glucose level is within the normal range or increased during the first day. Subsequently, due to the consumption of glucose by microbial flora and neutrophils, the glucose level steadily decreases until it is completely absent, which indicates the long history of the pathological process. Glucose level testing is important for assessing the effectiveness of bacterial meningitis treatment. With effective antibacterial therapy, the glucose level normalizes after 2-3 days, and if there is no effect, it remains reduced or decreases even more.

Among the additional research methods that are currently being implemented in practice as differential diagnostic express tests, it is recommended to determine the lactate level and pH of the cerebrospinal fluid. Normally, the lactate content is 1.2-2.2 mmol/l, with bacterial meningitis its level increases by 3-10 times or more. Normally, the cerebrospinal fluid has a slightly alkaline reaction, pH 7.35-7.40, with bacterial meningitis the pH level decreases to 7.0-7.1.

The concentration of glucose decreases as the cerebrospinal fluid circulates from the cerebral ventricles to the lumbar cistern. Normally, the ratio between the concentration of glucose in the lumbar cistern fluid and in the blood plasma is at least 0.6. It should be remembered, however, that the ratio of the concentration of glucose in the cerebrospinal fluid to the concentration in plasma may decrease for some time (approximately 2 hours) after eating. At very high glucose levels in the blood (over 25 mmol/l), the membrane glucose transporters are completely saturated, and therefore its relative concentration in the fluid may be lower than theoretically expected. A normal level of glucose in the cerebrospinal fluid with an elevated level in the blood may indicate increased utilization of glucose in the subarachnoid space. Low glucose levels in the cerebrospinal fluid may be observed in hypoglycemia, but the cerebrospinal fluid/plasma ratio remains unchanged. Much more often, hypoglycorrachia, i.e. low glucose content in the subthecal space, occurs due to impaired active membrane transport, which is accompanied by a decrease in the cerebrospinal fluid/plasma ratio. This is observed in many inflammatory processes in the meninges. Thus, low glucose levels are caused by acute bacterial, tuberculous, fungal and carcinomatous meningitis. A less pronounced decrease in glucose concentration is often observed in sarcoidosis of the meninges, parasitic infections (cysticercosis and trichinosis) and meningitis caused by chemical factors. In viral meningitis (mumps, herpes, lymphocytic choriomeningitis), the glucose level decreases slightly and often remains normal. Subarachnoid hemorrhage also causes hypoglycorrachia, the mechanism of which remains unclear. A decrease in the concentration of glucose in the cerebrospinal fluid can persist for 2-3 weeks after normalization of cytosis in acute meningitis.

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