Dog has low protein
Low protein could mean many things. I guess right at the onset I would start monitoring for weight loss as being the biggest indicator of whether this is a more serious problem.
Low protein means he is either not eating enough protein or if he is, he is either not digesting it or absorbing it properly. Secondly if that is not the problem, he may be losing it before he can utilize it eg he may be losing large quantities when he pees, which would indicate a problem with kidney function.
Both conditions have very different meanings and diagnostic approaches and treatments and would require a lot of factors to examine including doing a stool parasite test, do a urine test to test check for protein levels in the urine, examining the possibility of food or digestion intolerances or deficiencies.
It is likely that a recheck on blood will need to be run in the near future and that a step by step approach would need to be taken to determine whether low protein in this case was an incidental finding or whether it indicates something medical.
Good luck and remember to monitor the weight weekly - it will be a good indicator. Let your vet guide you on the direction to follow.
Martin Slome DVM