How can I tell if I have dcis?

Cannot. Lcis and dcis are both conditions are variants of changes in the breast that can only be determined by biopsy.
Biopsy. An overwhelming majority of cases of dcis are diagnosed in women who have an abnormality seen on mammography in the absence of any palpable lumps. It is believed that the significant increase in dcis over the past 20 years is due to the increased mammography screening over this time period.