How it works is that blue shield (with employers I've typically always had blue shield in California) sends a statement saying your doctor visit cost $XXXX, blue shield will pay $YYY and this will credit $ZZZ towards your annual out of pocket total.
But $XXXX - $YYY > $ZZZ, so what I actually had to pay to the doctor was more than blue shield credits me for having paid. So at the end of the year what I've actually had to pay has been well above the so-called "out of pocket maximum".
It doesn't happen most years (to me), but has happened on multiple years.
Labs that don't have a clear medical justification are probably easy to end up paying for out of pocket without getting the amount counted against the out of pocket insurance limit.
Would expect that to be clearly delineated on the bills though.
"maximum out of pocket" does not mean what any normal person would interpret it to mean. More than one year I have had to pay way more than the "maximum out of pocket".
The insurance company gets to decide unilaterally how much of what you pay out of pocket is credited toward their tally of what you supposedly paid out of pocket. In several years I've paid a lot more out of pocket than what the insurance statement credits me for having paid.