Yes, there's a test to see if you have a problem with vitamin absorption. Standard blood tests show if the vitamin is in your system, but not if there are absorption problems. The specialized test I had done was expensive around $400. I can write the name of the test if you want it. I had vials of blood drawn for it. Although I had some vitamin/mineral deficiencies, the only absoption problem that showed was with vitamin A. It is a coincidence your doctor prescribed a retin-a type cream, which is a substitute for vitamin A.
So you don't miss it, someone just asked for your doctor's name in the post above mine.