When I first started getting annual blood tests there were two values in particular that were consistently elevated. A bunch more tests and some specialist visits later the explanation was that I have a harmless genetic mutation that just causes those values to be high.
A few years back I had some different values pop high. They implied scary things. More specialist visits than before. A lot more tests. After months of that all of the scary things were eventually ruled out. And then the values went back to normal. Nobody has an explanation even now.
This is just with a pretty standard battery of tests: CBC with differential, comprehensive metabolic panel, lipid panel, TSH with reflex, vitamin D. They catch enough bad things that they're generally worth ordering on a regular basis for healthy people at annual physicals. The occasional wild goose chases like what happened with me is the price we pay for catching the more serious things.
I guess we'll see just how valuable monthly whole body ultrasounds are. There's a real risk that it will catch a lot of benign things without catching enough serious things.