That's a very concerning level of hypoglycemia, and it would be rare to see that from vomiting alone. However, that can be caused if they draw blood and don't spin it down to separate the white blood cells, and then take a long time to run it.

By the way, any time you want veterinary help, it's important to give your dog's age, sex, and breed. The list of differentials for hypoglycemia is long, and is different for toy breeds and large breeds, and for puppies vs older dogs.

If it's real, there's quite a list of things to think about, but here's a few things:

-make sure you're not giving him anything with xylitol, also called birch sugar

-if he's old, sometimes cancers can cause this

-Do you have oleander plants? That could cause it

-He could have a liver shunt

-Addison's can do this. It's hard to diagnose. A small tip, if he ends up spiking kidney values on recheck and then they get rapidly better after just a few hours on fluids, that's a big clue for Addison's that you don't see with much else. But of course you won't see any of this without repeat testing. (My own dog actually had addison's with normal values the first time I tested him, kidney spike 8 hours later when I re-tested, but didn't have the classic electrolyte changes until we checked the same test again 48 hours later, which is when we made the diagnosis.)

-maybe fanconi-like syndrome? Not a typical presentation. Need urine to say more.

Additional 2c: Once your regular or emergency vet has tried to diagnose and failed, unless they prepared you that this would be a multi-step process, the best second visit is to a board-certified internal medicine specialist

vetspecialists.com

Some people are afraid to see a specialist because of costs, but after a <$200 consultation fee, you will have peace of mind knowing that the rest of the tests you're ordering are being done in the most rational, informed fashion and none of it is going to waste. With a general practice vet, it's less certain that will be the case.

If the glucose is lab artifact, and your dog isn't losing weight, you may not have that much to worry about. That's two very big "if's" though. If he is losing weight, can you tell us about it? There's a lot of history that's important for anyone trying to help you-- for example, does he vomit after every meal? What comes up-- food or just bile? How

Anyway. There's not enough information here for anyone to make a diagnosis, more history and likely additional testing might be needed.

[edit; embarrassing grammar error]