I took a urine test and they said it had a trace of blood, why is that?!

I took a urine test and they said it had a trace of blood, why is that?

I TOOK A URINE TEST YESTERDAY AND THEY TOLD ME IT HAD A SMALL TRACE OF BLOOD IN IT, THEY SAID IT COULD HAVE BEENFROM DEHYDRATIN BECAUSE I HAVE BEEN WORKING OUT SO THEY TOLD ME TO DRINK LOTS OF WATER AND COME BACK TODAY TO RETEST, SO I DID AND THEY TOLD ME I STILL HAD A SMALL TRACE, NOT AS MUCH AS YESTERDAY BUT IT WAS STILL THERE AND I NEED TO GO SEE MY PRIMARY DOCTOR TO SEE WHAT IT WAS, DOES ANYONE KNOW WHY THIS HAPPENSOR WHAT CAUSES IT? SHOULD I BE WORRIED? I CANT SEE ANY BLOOD IN MY PEE WHEN I LOOK AT IT.

You probably have nothing to worry about. If you really did a hard workout recently before the test, than broken down muscle protein (myoglobin) can be misinterpreted by standard urine tests as blood. Your doctor can measure myoglobin in the urine separately to be sure. Trace blood is usually not much to worry about anyways.