Go see your doctor: Black stool is worrisome for bleeding in stomach/intestine/colon (although can also be caused by peptobismol etc). Black stool is not due to a kidney problem. Your doctor can do simple urine test to look for protein (and refer you to gastroenterologist for colonoscopy). More important to work w/doc to get to bottom of what's troubling you. Good luck!
Answered 7/22/2013
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4 doctors weighed in across 3 answers
4 doctors weighed in across 2 answers
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