There is a test you can get:
http://www.nlm.nih.gov/medlineplus/e...cle/003570.htm

It is not done often though. Tests that are not commonly run may have poor calibration on the machines because the "known sample" degrades with time.

I started taking 8000IU of vitamin A acetate (from Target's) (RDA amount 160%--and not high) because I had a history of poor conversion of betacarotene --a thyroid problem. I had orange hands and feet...

But my symptoms started to really reflect Vit A problems recently so I tried a modest dose and within a month I had huge improvements. Now I find some articles claiming older patients may have a hidden Vitamin A deficiency due to poor conversion of betacarotene.

The skin, eyes, mucus membranes, hair loss, etc.
http://lpi.oregonstate.edu/mic/vitamins/vitamin-A

My eyes have stopped burning since I started this..just a few months ago.
Most multivitamins have a majority of betacarotene in them, and not Retinol... so they really don't help those who are poor converters or poor absorbers.

Just keep in mind to not increase doses, and do this supplement modestly. I didn't get tested for it though.