If irregular shedding of the endometrium is suspected, an endometrial biopsy is performed on the 5th to 6th day after menstruation and the diagnosis is made if a secretory-responsive endometrium can still be seen in the midst of the uterus. This is because the secretory endometrium is completely shed by the 3rd to 4th day of normal menstruation. Patients with this condition often present with a mixed endometrium, i.e. a mixture of residual secretory endometrium with haemorrhagic necrotic tissue and new growths.
Some areas of the endometrium are still bleeding and this is the right time to take a biopsy so it should be done 5-6 days after the onset of menstruation for a better judgement of the accuracy of the disease diagnosis.