With the engine cool remove the cap - Is it full to the neck in the radiator? If so - that's good.
You could have had some bubbles in the lines which are still working out through the cooling system (recent coolant change?)
How much you are losing?... If it never needed filling it wouldn't need to be checked.
A very small amount can be normal. It can also be a very minor leak in a hard to see place.
There are many places hard to see, so not seeing anything obvious means only there is nothing obvious to see.
It doesn't mean there isn't a leak.
On a hot engine, coolant evaporates, which is why a dye is sometimes used to track down pesky leaks.
The car could also be burning coolant if there is a head gasket issue. Does your oil look good?
My oil as far as I see looks great.
The rad itself full every time I open it.
Also the upper turbo tank is full.
I didn't changed recently the coolant, I'm with mishi rad and stat, and it is winter here now ,could be cause the very low temps outside and the stat open very early.
I add half acup maybe ,no more than that.
Coolant is temperature sensitive, so if you noticed the change along with lower temps that could be part of it.
If it continues, you likely have a small leak that if you can't find is only a problem if you run out of coolant.
If it gets worse, you will likely more easily be able to find the leak...