Regarding further investigation of a disorder. What is the…

Hi,

Welcome to JA and thanks for this question. Actually, there is no one test which would be able to diagnose a metabolic derangement or an infection of the brain as these diagnoses would be made on the basis of some tests. For example, if we are suspecting an infection of the brain then we would do,

Spinal tap/Lumbar puncture - in which fluid is removed from the spine (the fluid is called CSF or cerebrospinal fluid) and that fluid is tested for various things which would include CSF routine examination, CSF culture, CSF gram stain for bacteria, CSF PCR for detection of various viruses.

MRI of the brain with contrast (to look for areas of the brain or the meninges which may be inflamed - the meninge sare the coverings of the brain and they can get inflamed in conditions like meningitis)

EEG - which looks at the electrical activity of the brain. This may be deranged in certain infections like viral encephalitis which can cause a specific cause of waveforms to appear

Whereas in case of metabolic derangements which can lead to a patient becoming drowsy, delirious or even unconscious, we would primarily do blood tests which would include (but not be limited to)

Liver function tests and ammonia levels - as liver failure can cause neurological impairment

Renal function tests - as renal failure can cause a patient to lose consciousness

Electrolyte levels - low sodium, calcium derangements, potassium derangements or even magnesium issues can impair the conscious level in some cases

Arterial blood gases - a low body pH or high pH can cause a patient to be drowsy or unconscious

There are many other metabolic causes for neurological impairment and they may be tested for with various tests.

In short there is no one test which would help a doctor determine what is the actual cause for a patients neurological problem, usually, it is a combination of tests. However, if we want to differentiate between a CNS infection and a metabolic cause, then the lumbar puncture would be the first test we do. If the lumbar puncture is negative then we would consider that the problem is due to a metabolic cause and if it is not, then further testing would be done on the same spinal fluid to isolate the infective organism.

Do you have any more questions?

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