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