Normal CSF contains a small number of lymphocytes and monocytes in a ratio of approximately 70:30 in adults. A higher proportion of monocytes is present in young children. An increase in the number of WBCs in CSF is termed pleocytosis. Disease processes may lead to abrupt increases or decreases in numbers of cells.

CSF is examined for the presence of RBCs and WBCs. The cells are counted and identified by cell type; the percentage of cell type is compared with the total number of WBCs or RBCs present. In general, inflammatory disease, hemorrhage, neoplasms, and trauma cause an elevated WBC count.

Normal CSF is essentially free of cells (Tables 5.5 and 5.6).

Adult: 0–5 WBCs/μL or 0–5 × 10⁶ WBCs/L

Newborn: 0–30 WBCs/μL or 0–30 × 10⁶ WBCs/L

Child: 0–15 WBCs/μL or 0–15 × 10⁶ WBCs/L

1. A lumbar puncture is performed (see Lumbar Puncture [Spinal Tap]).

2. Typically, approximately 20 mL of CSF is obtained and subsequently divided into four separate sterile screw-top tubes.

3. One of the tubes is used for counting the cells present in the CSF sample. The cells are counted by a manual counting chamber or by electronic means. A CSF smear is made, and various types of cells present are counted to determine differentiation of cells.

1. The total CSF cell count (includes neutrophils, lymphocytes, mixed cells, and cells after hemorrhage) is the most sensitive index of acute inflammation of the CNS.

2. WBC counts more than 500 WBCs/μL or more than 500 × 10⁶ WBCs/L usually arise from a purulent infection and are predominantly granulocytes (i.e., neutrophils). Neutrophilic reaction classically suggests meningitis caused by a pyogenic organism, in which case the WBC count can exceed 1000 WBCs/μL or 1000 × 10⁶ WBCs/L and even reach 20,000 WBCs/μL or 20,000 × 10⁶ WBCs/L.

   1. Increases in neutrophils are associated with the following conditions:

      1. Bacterial meningitis (Table 5.7)

      2. Early viral meningitis

      3. Early tubercular meningitis

      4. Fungal mycotic meningitis

      5. Amebic encephalomyelitis

      6. Early stages of cerebral abscess

   2. Noninfectious causes of neutrophilia include the following:

      1. Reaction to CNS hemorrhage

      2. Injection of foreign materials into the subarachnoid space (e.g., x-ray contrast medium, anticancer drugs)

      3. Metastatic tumor in contact with CSF

      4. Reaction to repeated lumbar puncture

3. WBC counts of 300–500/μL or 300–500 × 10⁶/L with preponderantly lymphocytes are indicative of the following conditions:

   1. Viral meningitis

   2. Syphilis of CNS (i.e., meningoencephalitis)

   3. Tuberculous meningitis

   4. Parasitic infestation of the CNS

   5. Bacterial meningitis due to unusual organisms (e.g., Listeria species)

   6. MS (reactive lymph present)

   7. Encephalopathy caused by drug abuse

   8. Guillain-Barré syndrome (15%)

   9. Acute disseminated encephalomyelitis

   10. Sarcoidosis of meninges

   11. Human T-lymphotropic virus type III

   12. Aseptic meningitis due to peptic focus adjacent to meninges

   13. Fungal meningitis

   14. Polyneuritis

4. WBC counts with greater or equal to 40% monocytes occur in the following conditions:

   1. Chronic bacterial meningitis

   2. Toxoplasmosis and amebic meningitis

   3. MS

   4. Rupture of brain abscess

5. Malignant cells (lymphocytes or histiocytes) may be present with primary and metastatic brain tumors, especially when there is meningeal extension.

6. Increased numbers of plasma cells occur in the following conditions:

   1. Acute viral infections

   2. MS

   3. Sarcoidosis

   4. Syphilitic meningoencephalitis

   5. Subacute sclerosing panencephalitis (SSPE)

   6. Tuberculous meningitis

   7. Parasitic infestations of CSF

   8. Guillain-Barré syndrome

   9. Lymphocytic reactions

7. Plasma cells are responsible for an increase in IgG and altered patterns in immunoelectrophoresis.

8. Macrophages are present in tuberculous or viral meningitis and in reactions to erythrocytes, foreign substances, or lipids in the CSF.

9. Ependymal (neuronal support cell) and plexus cells may be present after surgical procedures or trauma to the CNS (not clinically significant).

10. Blast cells appear in CSF when acute leukemia is present (lymphoblasts or myeloblasts).

11. Eosinophils are present in the following conditions:

    1. Parasitic infections

    2. Fungal infections

    3. Rickettsial infections (Rocky Mountain spotted fever)

    4. Idiopathic hypereosinophilic syndrome

    5. Reaction to foreign materials in CSF (e.g., drugs, shunts)

    6. Sarcoidosis

Pretest Patient Care

1. Follow pretest patient care for lumbar puncture (see Lumbar Puncture [Spinal Tap]).

2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. Patient position or movement, such as that caused by crying, gasping, or coughing, may cause changes in CSF pressure.

2. Delay in time from collection to testing may affect results.