Blood cells detected in urine - Nishmat Yoatzot Halacha

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Blood cells detected in urine

October 22, 2025

Question

I work in a clinic and check pregnant women's urine using a dipstick. Sometimes the strip turns a green colour, indicating the presence of red blood cells. I am wondering if this has any implication for the dati women. It's not that I'm seeing blood, and they aren't either – just an indication of red blood cells.

Answer

To make a woman niddah, blood must be one of the niddah colors. Red blood cells such as you describe do not make a woman niddah, since there are not enough of them to make the urine a niddah color. (Even blood that is clearly visible in the urine does not always make a woman niddah, depending on the source. A specific halachic question should be asked in such a case.)

Please write back with any further questions.