Talk to your doctor. They can take a blood test and send it off to analysis. It can be somewhat expensive. When I said "all at once" I didn't mean that a simple biochemical test can reveal all deficiencies, obviously, but that a single blood test can be sent off to have many different tests done. I'm not yet sure exactly how it works in the US, sorry.

The kind of deficiencies I had in mind would be vitamin (e.g. D, K), mineral (e.g. iron, calcium) and electolytic (e.g. magnesium, potassium).