There are two possible ways that blood could get into the urine.  First, if the glomerulus was in some way damaged, its efficiency as a filter may be somewhat compromised.  If this was the case, RBCs, protein, and other larger particles could get into the urine.  However, in this case, the high blood result with only trace amounts of protein suggests that the problem did not occur at the glomerulus.  This leads to the other cause of blood in the urine: damage to the urinary tract.  If any part of the urinary tract is damaged, blood could get into the urine, even if the glomerulus is working fine.  Renal calculi, or kidney stones, could cause damage to the renal tubules as they flow down the urinary tract.  This damage would explain the presence of blood (in the absence of large amounts of protein).

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