Normal cerebrospinal fluid, or CSF, is clear and colorless. Both infectious and non-infectious processes can alter the appearance of the cerebrospinal fluid. In this video, taken from our Body Fluid Lab Essentials course, we review what the gross appearance and cell count can tell you about the cerebrospinal fluid and critical clues you need to be on the lookout for.
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Normal cerebral spinal fluid, or CSF is clear and colorless. Both infectious and non-infectious processes can alter the appearance of the cerebral spinal fluid. Cerebral spinal fluid will appear turbid if as few as 200 white blood cells per microliter, or 400 red blood cells per microliter are present. Cerebral spinal fluid will appear grossly bloody if 6000 or more red blood cells per microliter are present.
Red blood cells rapidly lies after entry into cerebral spinal fluid, and cause xanthochromia, a discoloration of the cerebral spinal fluid. The breakdown of hemoglobin first to oxyhemoglobin, which appears pink and later to bilirubin, which appears yellow leads to the yellow or pink discoloration of the cerebral spinal fluid, known as xanthochromia.
Xanthochromia is often used in the diagnosis of subarachnoid hemorrhage since xanthochromia can be detected as soon as two to four hours after red blood cells have entered the subarachnoid space. This means that as long as the lumbar puncture is performed at least six hours after the onset of the headache, the presence of xanthochromia is likely due to a subarachnoid hemorrhage, and not likely due to a traumatic tap, where the fluid would be frankly bloody, and xanthochromia would not yet be present.
Xanthochromia can also occur when the protein concentration of the cerebral spinal fluid is elevated above 150 milligrams per deciliter, or may be caused by brain tumors, stroke, Guillain-Barre syndrome and systemic disorders such as diabetes mellitus, and hypothyroidism. Xanthochromia can also occur with systemic hyperbilirubinemia, defined as a serum bilirubin greater than 10 to 15 milligrams per deciliter, due to liver disease. The cell count can be useful because cerebral spinal fluid is normally acellular.
However, up to five white blood cells, and five red blood cells per microliter are considered normal in adults when the cerebral spinal fluid is sampled by lumbar puncture. The presence of more than three polymorphonuclear leukocytes per microliter in CSF is abnormal in adults, and indicates an infection. An elevated CSF white blood cell concentration does not diagnose an infection since increases in the CSF white blood cell concentration can occur in a variety of inflammatory states that can be infectious or non-infectious.
The following caveats about the interpretation of cerebral spinal fluid cell counts may be useful. The cerebral spinal fluid cell count must always be correlated with clinical findings. Polymorphonuclear leukocytes predominate in the cerebral spinal fluid of as many as two thirds of patients with viral meningitis due to enteroviruses. In these patients, a shift to lymphocytic predominance usually occurs within 12 to 24 hours. In comparison, bacterial meningitis is characterized by the presence of neutrophils in the CSF. Lastly, note that the presence of eosinophils in the cerebral spinal fluid has limited diagnostic utility.