ELISA would not be better. Check out the Wikipedia article on glucometers. It gives the details you want. You also want to look up glycosylated hemoglobin (HgA1c).This is actually quite an interesting topic; I'm a biochemistry student so I'd be interested in finding out which 'chemical reagents' are used. There are simple chemical tests for glucose but I wonder if an ELISA (Enzyme-Linked Immunosorbent Assay) is a better option.
Indeed I haven't heard of an ELISA for glucose but a vast number of antibodies have been isolated or developed, I'm sure there's one for glucose somewhere. But the only real reason for using an ELISA over other methods would be specificity to avoid false positives, or to produce a more linear relationship between glucose conc. and the absorption of a specific wavelength on the EM spectrum once combined with a reagent. If an ELISA doesn't improve these factors then it's unnecessarily complicating the test.I guess that you could produce an ELISA (I don't know of one) on the assumption that you could produce a suitable antibody to glucose and then successfully conjugate it to a suitable enzyme such as HRP. We then used to use Phenolphthalein Monophosphate as a color reagent. Of course if you got a suitable antibody then the world is open to any technique you like such as FIA or RIA.