I have sent oil to
Blackstone Labs. I have in Fort Wayne (where they are located) and pass their shop frequently. I highly recommend them. They usually have the results within a few hours of dropping it off. Obviously if you mail it in it takes longer to get there but they will e-mail you the PDF results.
The cooling system is a closed system, so technically any coolant loss is a sign of problems. But in reality, small leaks, evaporation, etc happen. That much coolant though may be a sign of something more though. It also may just mean that you had a decent sized air bubble that just worked its way out and the coolant replaced it.
Remember that as your engine heats and cools, gaps around gaskets can form allowing coolant to escape. If the coolant escapes while the engine is hot, most of the coolant will evaporate on contact. You wouldn't ever see a puddle on the ground. When my intake gasket (and later head gasket) leaked, I would rarely see a puddle...only when I would take a short trip building system pressure but not heating the block to a high enough temperature to boil off the leaking coolant.
The easy check to see if you have coolant in your oil is to look on the underneith side of your oil cap. If you see any goopy substance, often described as runny mayo, you have a leak. You may also show signs of it just inside the filler hole on the valve cover. The lack of the "mayo" doesn't disprove the presence of antifreeze though. Sending a sample into Blackstone is your best bet...a $20 test is much better then $2000 engine.
The test also will tell you a general overall health of your system. High levels of particular metals may indicate particular areas that need looked at and addressed. When I did my last test to confirm my leaky intake gasket, they said my lead levels were high, most likely from the antifreeze prematurely wearing the bearings.