Slab Moisture Test

Can anyone recommend a reputable company that provides moisture tests for concrete slabs?

We just had our slab tested by a 'big box' store (that actually uses a 3rd party company) and the simple test they use came back 'red'. Don't want to make a go/no-go decision on using engineered wood flooring based on a single data point...

Recommendations/thoughts can be emailed to geichlersv@yahoo.com.

Thanks.