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Introduction ⬇

Albumin composes most (50%–75%) of the proteins in CSF. The albumin and IgG that are present in normal CSF are derived from the serum. Increased levels of either or both are indicative of damage to the blood–CNS barrier.

The combined measurement of albumin and IgG is used to evaluate the integrity and permeability of the blood–CSF barrier and to measure the synthesis of IgG within the CNS. The IgG index is the most sensitive method to determine local CNS synthesis of IgG and to detect increased permeability of the blood–CNS barrier.

The IgG index method is superior to the IgG-to-albumin ratio or measurement of IgG only.

Normal Findings ⬆ ⬇

Albumin: 10–35 mg/dL or 1.5–5.3 μmol/L

IgG: <4.0 mg/dL or <40 mg/L

CSF serum albumin index: <9.0

CSF IgG index: <0.60

CSF IgG index = (CSF IgG × serum albumin)/(serum IgG × CSF albumin)

CSF-to-serum IgG ratio: <0.003

Procedure ⬆ ⬇

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

  2. Obtain 0.5 mL of CSF in a sterile screw-top tube.

  3. Freeze the sample if the determination is not done immediately.

Clinical Implications ⬆ ⬇

  1. Increased CSF albumin occurs in most of the same conditions as increased total protein, especially:

    1. Lesions of the choroid plexus

    2. Blockage of CSF flow

    3. Bacterial meningitis

    4. Guillain-Barré syndrome

    5. Many infectious diseases, such as typhoid fever, tularemia, diphtheria, and septicemia

    6. Malignant neoplasms of the CNS

  2. CSF serum albumin index:

    1. An index of less than 9.0 is consistent with an intact blood–brain barrier.

    2. An index between 9 and 14 is considered slight impairment to the barrier.

    3. An index from 15 to 30 is considered moderate impairment of the barrier.

    4. An index of more than 30 is severe impairment.

  3. Increased CSF IgG index occurs in the following conditions:

    1. MS

    2. Subacute sclerosing leukoencephalitis

    3. Neurosyphilis

    4. Chronic phases of CNS infections (SSPE)

Interventions ⬆ ⬇

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.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed to prevent and detect complications.

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

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

A traumatic tap will invalidate the results.