“Lumbar Puncture: Creating headaches not only for the patient…”


25 years ago, examination of cerebro-spinal fluid (CSF) was a fairly straightforward process. You got a cell count, Gram stain, protein and glucose levels. For the really complex patient you might have added a couple more tests like an Indian Ink or a TB culture.

Not any more….

There are now dozens of tests that can potentially be performed on CSF, most of them molecular, and a particular increase in viral PCR, e.g HSV, EBV, CMV, VZV, HHV6, etc. etc. The acronymical list goes on…

If you work in a clinical microbiology lab, then the chances are you will have come across one of the following scenarios:

  • A CSF sample arrives into the lab with a long list of molecular tests requested. The cell counts, protein and glucose are then completely normal on initial testing.
  • A CSF sample arrives into the lab with a long list of molecular tests requested by a doctor who is in the process of studying for post-graduate exams and wants to show off his/her expertise.
  • A CSF sample arrives into the lab with a long list of molecular tests requested. By the time some of these tests are performed, the patient has long recovered and is sitting at home watching ER with a glass of wine in hand.

CSF testing can now be fairly problematic. Cost issues, poor positive predictive value of individual tests, available CSF volume, distributing bits of CSF to different reference labs, lack of clinical details can all contribute to this headache. Not to mention that the results of these tests often have little or no direct effect on the management of the patient. 

I am convinced that there are huge numbers of molecular tests performed on CSF samples which turn out to be completely unnecessary.

Good communication between the laboratory and clinicians is obviously key, but I also believe that more and more the laboratory needs to become the gatekeeper for complex CSF testing, as opposed to being the submissive, and passive recipient of such requests.


I have added a short powerpoint on toxoplasmosis to the website

2 thoughts on ““Lumbar Puncture: Creating headaches not only for the patient…”

  1. Very true. I’m a hospital doctor now doing some research time with microbiology, but previous did some work looking at ANCA gating in immunology, as it was probably fairly similar – everyone with ‘funny weakness’ seemed to be getting an ANCA.

    Prior to doing labtime, I had very little insight into how resource intensive these tests can be- you sort of assume that it’s like adding on a calcium level- you just put the sample in a big machine and a result comes out… ‘How not to test’ is a real clinical art, I think you have to learn with experience. Out of medschool, the exam process measures your ability to list all the causes, so the best answer for a possible peripheral neuropathy is to list and test for everything which earns you full marks…
    Some gatekeeping is definitely necessary. Often the best way was to have a specialist opinion to provide the reassurance that the clinician is seeking from ‘overtesting’ – just writing in the notes ‘this is clearly not xxxx, but it would be worth testing for y and z’.
    This blog reply brought to you in apology for all the ‘immune screen’s and ‘viral screen’s I’ve ordered in the past….

    1. Thanks for your comments Nicola, I am just coming back to this much neglected website of mine to see how I can develop it further. You might also be interested in this post

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