If they think if there is a potential problem, they run another test - which is what happened to me last summer.
The results came back at something like 19, and Doc said that anything under 30 was 'no cause for concern'.
Of course, I then spent a while ransacking Google for more info, and I can't really say things became much clearer. However I am pretty sure that protein in urine is only a concern if it gets too high - which is why the actual numbers are so important.