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Introduction ⬇

The CSF glucose level varies with the blood glucose levels. It is usually about 60% of the blood glucose level. A blood glucose specimen should be obtained at least 60 minutes before lumbar puncture for comparisons. Any changes in blood sugar are reflected in the CSF approximately 1 hour later because of the lag in CSF glucose equilibrium time.

This measurement is helpful in determining impaired transport of glucose from plasma to CSF, increased use of glucose in the CNS, and glucose use by leukocytes and microorganisms. The finding of a markedly decreased CSF glucose level accompanied by an increased WBC count with a large percentage of neutrophils is indicative of bacterial meningitis.

Normal Findings ⬆ ⬇

Adult: 40–70 mg/dL or 2.2–3.9 mmol/L

Child: 60–80 mg/dL or 3.3–4.4 mmol/L

CSF-to-plasma glucose ratio: <0.5

CSF glucose level: 60%–70% of blood glucose levels

Clinical Alert

The critical value for CSF glucose level is more than 20 mg/dL (1.1 mmol/L); below this level, damage to the CNS will occur

Procedure ⬆ ⬇

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

  2. Place 1 mL of CSF in a sterile screw-top tube. The glucose test should be done on tube 1 when three tubes of CSF are taken. Accurate evaluation of CSF glucose requires a plasma glucose measurement. A blood glucose level ideally should be drawn 1 hour before the lumbar puncture.

Clinical Implications ⬆ ⬇

  1. Decreased CSF glucose levels are associated with the following conditions:

    1. Acute bacterial meningitis

    2. Tuberculous, fungal, and amebic meningitis

    3. Systemic hypoglycemia

    4. Subarachnoid hemorrhage

  2. CSF glucose levels are uncommonly decreased in the following conditions:

    1. Malignant tumor with meningeal involvement

    2. Acute syphilitic meningitis

    3. Nonbacterial meningoencephalitis

  3. Increased CSF glucose levels are associated with the following conditions:

    1. Diabetic hyperglycemia

    2. Increased serum glucose

    3. Epidemic encephalitis

Clinical Alert

  1. Decreased glucose levels reflect abnormal activity due to infectious microorganisms metabolizing glucose.

  2. The findings of a markedly decreased CSF glucose and an increased WBC count with a high percentage of neutrophils are indicative of bacterial meningitis.

Interventions ⬆ ⬇

Pretest Patient Care

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

  2. Explain the need for a blood specimen test for glucose to compare with CSF glucose.

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

Posttest Patient Care

  1. Review abnormal CSF glucose levels; report and record findings. Modify the nursing care plan as needed to prevent complications. Correlate with the presence of meningitis, cancer, hemorrhage, and diabetes.

  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 ⬆

  1. Falsely decreased levels may be due to cellular and bacterial metabolism if the test is not performed immediately after specimen collection.

  2. A traumatic tap may produce misleading results owing to glucose present in blood.

  3. see Appendix E for drugs that affect test outcomes.