hi sandy it depends on your coverage, where you live etc.
i live in ontario canada, where a lot of lab work is covered by the provincial health plan - here is the list of what testing can be done here:
biochemistry (includes vitamin a, zinc, potassium, sodium, uric acid, etc)
http://www.health.gov.on.ca/english/pro ... bfbio.html
immunoassays (includes vitamin D3 -both 25-hydroxy and 1,25 dihydroxy, aldosterone, cortisol, ferritin, etc)
http://www.health.gov.on.ca/english/pro ... bfimm.html
hematology (includes vitamin b12, RBC, WBC, prothrombin time, etc)
http://www.health.gov.on.ca/english/pro ... bfhem.html
there are more categories but i don't really use these: Immunohematology, Immunology; Microbiology; Anatomical Pathology, Histology and Cytology
to date i have tested several things that are not covered.
the first was homocysteine, back at the veeeerrrry beginning of my learning curve when i didn't really understand the whole b12 deal too well. the second and third have been selenium, and vitamin E (alpha tocopherol). the homocysteine and vitamin E cost $30 each, and the selenium was $35.
personally i ask my doctor for lab requisitions for the ms 'usual suspect' things that i like to test (that process is easier now but started with me bringing in a lot of journal literature to support a request), and she does me up the requisition.
so then i stop taking any supplements for a short 'washout', take the req to the lab, and the results come back 'normal'.
'normal' is only good enough for healthy ppl not sick ones like us, so then you make sure to get actual numbers, with units.
then check your results against averages determined in 'health and disease' research (doesn't matter what disease you are just interested in the healthy controls), many of which have been posted here at some point or other, or you can just ask me. if i have already done the lit review and found a few good studies supporting a possible 'optimal' level for something you are testing, i can relay.