CSF is normally clear and colorless.

Normal CSF pressure in the lower back for an adult ranges from 90–180 millimeters (mm) water. For children younger than 8 years old, the normal opening pressure range is 10–100 mm water.

The normal protein content of CSF in an adult's lower back (lumbar) region is 15–45 milligrams per deciliter (mg/dL) or 150–450 milligrams per liter (mg/L). Older adults and children may have higher values that are still in the normal range.

The normal range for glucose content in the CSF is about 60% of the blood glucose level. The levels may be slightly increased if the person has just eaten.

Normal CSF contains no red blood cells (RBCs). The white blood cell (WBC) count for adults is 0–5 WBCs per cubic millimeter (mm³). Children may normally have a higher WBC count. No neutrophils are present.

No infectious organisms (such as bacteria, fungi, or a virus) are found in the CSF sample. No tumor cells are present.

Blood in the CSF can result from bleeding (hemorrhage) in or around the spinal cord or brain, but it may also be caused by tiny blood vessel poked during the spinal tap. If a brain hemorrhage has occurred, the color of the CSF may change from red to yellow to brown over several days. Bleeding caused by the lumbar puncture itself will show more red blood cells in the first sample collected than in later samples. Cloudy CSF may mean an infection (such as meningitis or a brain abscess) is present.

High CSF pressure may occur as a result of swelling (edema) or bleeding (hemorrhage) in the brain, infection (such as meningitis), stroke, or other circulatory problems. Below-normal pressure may mean a blocked spinal canal.

A high level of protein may be caused by bleeding in the CSF, a tumor or spread of a cancer from another area of the body, diabetes, infection, injury, Guillain-Barré syndrome, severe hypothyroidism, or other nerve diseases. An increase in antibodies (immunoglobulins) may be caused by inflammation in people who have multiple sclerosis, immune system disorders, or other bacterial and viral diseases.

Low glucose levels in the CSF are abnormal and may be caused by bacterial meningitis. Viral meningitis does not often cause low glucose levels in the CSF. Brain hemorrhage may also cause low glucose levels several days after bleeding begins. Higher-than-normal glucose levels are often caused by diabetes.

Red blood cells (RBCs) in the CSF can result from bleeding. High levels of white blood cells (WBCs) can indicate meningitis. Tumor cells and abnormal levels of white blood cells can show cancer is present.

Antibodies, bacteria, or other organisms in the CSF means that an infection (such as syphilis) or disease is present. Bacterial markers (bacterial antigens) that show up mean meningitis. Cultures or stains of the CSF may also help show the cause of meningitis or encephalitis.