CEREBROSPINAL FLUID ANALYSIS

47 CEREBROSPINAL FLUID ANALYSIS

Rick L. Cowell, James H. Meinkoth, Theresa E. Rizzi

1 List the two common sites for collection of cerebrospinal fluid (CSF) in dogs and cats.

a. Atlantooccipital space (cerebellomedullary cistern)

b. Lumbar subarachnoid space: between the fifth and sixth lumbar vertebrae (L5-6)

2 What determines which location to use for CSF collection?

Selection is based on the neurologic localization of the lesion. The atlantooccipital space (cerebellomedullary cistern) is used to collect CSF when the lesions are above the foramen magnum or for lesions of the extreme craniocervical spinal cord. The lumbar subarachnoid space, L5-6, is used as the site of CSF collection for lesions below the craniocervical spinal cord.

3 How much cerebrospinal fluid can be collected safely?

CSF can be collected safely up to approximately 0.2 ml of CSF/kg body weight.

4 Are there times when CSF collection is contraindicated?

CSF collection is contraindicated when anesthesia is contraindicated and in animals with increased intracranial pressure (ICP) because of the risk of brain herniation.

5 Describe normal cerebrospinal fluid.

CSF is a clear, colorless, transparent fluid with very low cellularity (almost acellular). Reference ranges are 0 to 5 cells/μl for dogs and 0 to 8 cells/μl for cats. Most normal dogs and cats have between 0 and 2 cells/μl. CSF also has very low protein concentration (10-20 mg/dl for CSF from atlantooccipital space; <40 mg/dl for CSF from L5-6).

7 What other tests are sometimes performed on a CSF analysis?

Other tests done on the CSF analysis include the Pandy test, various biochemical measurements (e.g., glucose, creatine kinase, lactate dehydrogenase), electrophoresis, and culture.

8 What is the Pandy test?

The Pandy test is a procedure to determine the presence of immunoglobulins in CSF. In normal animals, the Pandy test should be negative.

9 How is the Pandy test performed, and what is its sensitivity?

The Pandy test is performed by adding a few drops of CSF to 1 ml of 10% carboxylic acid (Pandy reagent). If turbidity develops, the test is positive (presence of immunoglobulins). The test has a sensitivity of about 50 mg immunoglobulin/dl CSF.

10 How quickly should cerebrospinal fluid be processed?

Cell counts and cytology smears should be done within 30 to 60 minutes of CSF collection.

11 Why does the CSF sample need to be processed so quickly?

The low protein concentration of CSF causes the cells to lyse quickly.

12 What if the CSF sample cannot be processed quickly?

If the CSF sample cannot be processed within 30 minutes, 40% ethanol can be added in a 1:1 ratio with the CSF to help preserve the cells. Other choices are adding plasma, 20% albumin, 4% to 10% neutral buffered formalin, or 50% to 90% alcohol in a 1:1 ratio with CSF. Also, adding 1 drop of 10% formalin to 1 to 2 ml of CSF has been suggested. Formalin will interfere with staining of the sample (Romanowsky stains), and many laboratories do not recommend its use. All these preservation measures will interfere with other tests (e.g., biochemical analysis) and will falsely decrease the cell count (dilution effect). The cell count is multiplied by two to correct for the dilution effect.

In addition, CSF samples are often split, and 40% ethanol (or one of the other choices) is added to one of the two sample halves to help preserve cells for cell counts and cytology. Ethanol (or other) is not added to the other sample half so that it can be used for other testing, such as protein concentration and biochemical analysis, which are relatively stable. Refrigeration of the sample also helps to slow down cell lysis.

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Tags: Veterinary Clinical Pathology Secrets

Aug 26, 2016 | Posted by admin in INTERNAL MEDICINE | Comments Off

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