Uterine bleeding can make a woman niddah, even when it is not menstrual. It is difficult to ascertain the nature of the staining from the doctor’s description as written here. That being said, staining (as opposed to a flow) is subject to halachic leniencies and often does not make a woman niddah, at any stage of life. For example, if the staining was found on colored undergarments or if the stains were smaller in size than a gris (roughly the area of the American dime or Israeli shekel), it did not make her niddah. For more information, please see our site’s article on stains, “Ketamim.”

A woman, at any stage of life, does not automatically become niddah from an endometrial biopsy. Uterine bleeding almost always results from an endometrial biopsy. Since this bleeding is caused by injury, the opinion of the posek of this site, R Yehuda Henkin, is that it does not render the woman niddah. The bleeding may go on for about a week, and for that time can be attributed to the procedure. Other authorities are less comfortable permitting bleeding that comes from the uterus, even if a clear source of injury is seen. Therefore, it would be best to ask for a specific ruling from her rabbi, if she has one.

For all procedures that enter the uterus, the size of the instrument that enters is also important. Instruments larger than a certain size render a woman niddah even if there is no bleeding. Opinions as to this size vary – R Henkin rules that an instrument with a diameter of 19mm or more would make a woman niddah. The catheter used for an endometrial biopsy is usually rather small, but one should double check with the physician as to what the actual size was.

Please write back with any further questions.