Hi,
In short it means you have some problem in the Kidney's filtering system. Short explanation: The kidney does two important jobs: 1. It filters out the wastes that are in the blood so it can be released ( = urine). 2. It also reabsorbs materials that the body still needs which got past the original filtering system. But you have to understand that as any filter it has the "screening size" therefor certain compounds (=particles) do not get past the filtering system of the kidney simply because they are too big (e.g: The Red & the white blood cells). If it passed we would need a blood transfusion every time we went to the bathroom..... God forbids.... As per Proteins: They are large molecules that have several very important duties in our body (e.g: Build the muscles, important role in building our immune system, just to name 2). Most proteins are also too large to pass through that filtering system of the kidney. And since they are not supposed to pass into the kidney, once they pass it they are gone (no mechanism for proteins to be reabsorbed). Therefore, if protein is detected in the urine, it means there is something going on with the filter (called the glomerulus) that is allowing the proteins to pass.
Best regards,