What does low protein in your blood mean?

Find cause. This may be as simple as a protein-poor diet (some of the fad / "green" diets can do this), or reflect low Albumin from liver disease, kidney protein wasting (nephrotic syndrome), myeloma, inflammatory bowel syndrome, or any of a host of illnesses. And some folks just genetically make little albumin. Good luck; a lab value means nothing out of context.