Concrete floor with bamboo flooring

[Mehale]

I have a bungalow from the late 1960s. It has a black asphalt base. The previous owners did a rear extension on the same room with a concrete slab. I plan to use bamboo flooring on an underlay over both surfaces.
The issue I have is that I have a basic moisture reader device (4 pins) and on the asphalt there is a zero reading. On the concrete base it’s showing 17%. Is this bad? Will the underlay advertised with ‘a dpm’ be sufficient or is it a gimmick?
I also want to put some self-levelling screed down because where the 2 materials join is slightly uneven etc

Thanks in advance

 

[dazlight]

Not sure what meter you are using but that’s not a correct reading.
how long has the concrete been down ? If that doesn’t have a damp proof membrane under it you could apply a liquid Dpm to it.