Cerebrospinal fluid collection and interpretation
Collect 2mLs of CSF into each tube.
If you are measuring opening pressure be familiar with the manometer equipment. This is done at the very beginning and the fluid collected is put into the first tube.
The following values are taken from The Royal College of Pathologists of Australasia and are in relation to normal versus viral or bacterial meningitis. Subarachnoid haemorrhage is discussed below.
Table 1: RCPA
For paediatic values and an overall paediatric focused Lumbar Puncture The Royal Children’s Hospital Melbourne has a great page detailing Lumbar Puncture Guideline.
Subarachnoid Haemorrhage (SAH):
In a non traumatic non contaminated sample CSF should not be more than 6 RBC.
An issue arises when there are greater than 5 x 106 but the the Lumbar Puncture was considered a traumatic tap. Are the RBCs present due to a subarachnoid bleed or your traumatic tap?
To date, there is no general consensus as to the threshold for determining a traumatic tap. The majority of clinicians are not confident to rely on decreasing measures of RBCs between the 1st and 4th tube of a CSF collected to confirm or deny a traumatic tap. Further investigation into this area is required.
Measuring Xanthochromia (Greek for ‘yellow colour’) is the current best way of distinguishing a traumatic tap from a true SAH, it is done by visual and spectrophotometric methods.
There are 2 things can cause CSF to have yellow colour/xanthochromia
Haemoglobin in CSF haemolyses within two to four hours producing oxyhaemoglobin. This process occurs both in vivo and in vitro. Oxyhaemoglobin is then converted to bilirubin by the enzyme haemoxygenase over a period of 12 hours (9–15 hours). This conversion for the most part takes place in vivo.
A traumatic tap can produce oxyhaemoglobin in the tube in vitro but bilirubin will not be formed.
- LP should be done at 12 hours post onset of headache when spectrophotometry is done, visual xanthochromia can be done at 6 hours
- Promptly send CSF for analysis and spectrophotometry
- A subarachnoid haemorrhage is confirmed with both oxyhaemoglobin and bilirubin by spectrophotometry
- A traumatic tap can have oxyhaemoglobin ( visual xanthochromia) but no bilirubin (positive by xanthochromia)
- Visual xanthochromia holding the tube against white and pinkish/yellow colour suggests positive.
We recommend you review the evidence as presented in the video 'SAH' on the relative merit of both techniques.