Cerebrospinal fluid (CSF) is collected by performing a lumbar puncture on your patient. This is performed if the doctor suspects certain conditions such as meningitis or subarachnoid haemorrhage. You will not be expected to know this skill for examinations, however you may be asked to interpret some CSF results. This station tests your knowledge of both the normal values of various components of CSF, and also your ability to make a differential diagnosis of a condition purely from a set of CSF results. Subject steps The most important knowledge to have for this station are the normal values. The most important of these are given in the table below. Note that these are for adults only: Systematically you will now take the examiner through the results which have been given. Start at the top and comment whether each result is normal or not. If any result is abnormal, it should be commented whether the result is slightly or very deranged. Normal Range Appearance Clear & colourless White Cells 0 – 5 x 106 per litre (all lymphocytes with no neutrophils) Red Cells 0 – 10 x 106 per litre Protein 0.2 – 0.4 grammes per litre (or less than 1% of the serum protein concentration) Glucose 3.3 – 4.4 mmol per litre (or ≥ 60% of a simultaneously derived plasma glucose concentration) pH 7.31 Pressure 70 – 180 mmH2O Now it will be most likely that you are asked to make a differential diagnosis based upon the results given. A number of conditions give deranged CSF readings and therefore knowledge of which conditions affect the different values is vital. The changes in various conditions are given below: Bacterial Meningitis Appearance Cloudy & Turbid White Cells Raised neutrophils Red Cells Normal Protein High or Very High Glucose Very Low Viral Meningitis Appearance Normal White Cells Raised lymphocytes Red Cells Normal Protein Normal or High Glucose Normal or Low Tuberculous Meningitis Appearance Normal or Slightly Cloudy White Cells Raised lymphocytes Red Cells Normal Protein High or Very High Glucose Very Low Subarachnoid Haemorrhage Appearance Usually blood stained White Cells Normal Red Cells Very High Protein Normal or High Glucose Normal or Low Guillan-Barré Syndrome Appearance Normal White Cells Normal Red Cells Normal Protein High (only after one week) Glucose Normal or Low Multiple Sclerosis Appearance Normal White Cells Raised lymphocytes Red Cells Normal Protein High Glucose Normal Although initially daunting, obvious patterns will become recognisable. It is also more likely that you will be asked about the more common conditions, such as bacterial and viral meningitis. If the condition asked about is either kind of meningitis, it is most likely that a causative organism will be asked for. Therefore make sure to learn the common causes of meningitis for varying age groups as well as the treatment. Source
