section name header

Introduction ⬇

Although many different enzymes have been measured in CSF, only lactate dehydrogenase (LDH) appears useful clinically. Sources of LDH in normal CSF include diffusion across the blood–CSF barrier, diffusion across the brain–CSF barrier, and LDH activity in cellular elements of the CSF, such as leukocytes, bacteria, and tumor cells. Because the brain tissue is rich in LDH, damaged CNS tissue can cause increased levels of LDH in the CSF.

High levels of LDH occur in about 90% of cases of bacterial meningitis and in only 10% of cases of viral meningitis. When high levels of LDH do occur in viral meningitis, the condition is usually associated with encephalitis and a poor prognosis. Tests of LDH isoenzymes (LDH exists in four enzyme classes; two are cytochrome c–dependent enzymes and two are NAD[P]-dependent enzymes) have been used to improve the specificity of LDH measurements and are useful for making the differential diagnosis of viral versus bacterial meningitis (see Chapter 6 for a complete description of isoenzymes). Elevated LDH levels following resuscitation predict a poor outcome in patients with hypoxic brain injury.

Normal Findings ⬆ ⬇

Adults: <40 U/L or approximately 10% of serum levels (total LD activity)

Neonates: <70 U/L

Procedure ⬆ ⬇

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

  2. Obtain 1 mL of CSF for the LDH test in a sterile screw-top tube.

  3. Take the sample to the laboratory as quickly as possible.

Clinical Implications ⬆ ⬇

  1. Increased CSF LDH levels are associated with the following conditions:

    1. Bacterial meningitis (90% of cases)

    2. Viral meningitis (10% of cases)

    3. Massive stroke

    4. Leukemia or lymphoma with meningeal infiltration

    5. Metastatic carcinoma of the CNS

  2. The presence of CSF LDH isoenzymes 1, 2, and 3 reflects a CNS lymphocytic reaction, suggesting viral meningitis.

  3. The CSF LDH isoenzyme pattern reflects a granulocytic (neutrophilic) reaction with LDH isoenzymes 4 and 5, suggesting bacterial meningitis.

  4. High levels of CSF LDH isoenzymes 1 and 2 suggest extensive CNS damage and a poor prognosis (i.e., they are indicative of destruction of brain tissue).

  5. CSF LDH isoenzymes 3 and 4 suggest lymphatic leukemia or lymphoma.

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 abnormal LDH test patterns; report and record findings. Modify the nursing care plan as needed to appropriately detect and prevent 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 ⬆

For the LDH test to be valid, CSF must not be contaminated with blood. A traumatic lumbar tap will make results difficult to interpret.