DUB is defined as abnormal vaginal bleeding without an identifiable pathologic condition. This is in contrast to abnormal uterine bleeding (AUB), which results from a broad spectrum of conditions. In adolescents, DUB is most often due to the anovulatory cycles that result from an immature hypothalamic-pituitary-ovarian axis. Etiologies of AUB, which must be excluded, are numerous and include genital tract abnormalities (ovarian, fallopian tube, uterine, cervical, vaginal, and vulval), trauma, drugs (oral contraceptives, corticosteroids, chemotherapy, phenytoin [Dilantin], antipsychotics) and systemic diseases (Table 196.1). Optimal management of DUB requires a systematic diagnostic and therapeutic approach.

By definition, other causes of irregular menses must be excluded before a diagnosis of DUB can be made. In girls in whom a diagnosis of DUB is considered, additional evaluation may include follicle-stimulating hormone, luteinizing hormone, thyroid-stimulating hormone, and prolactin on day 3 of the menstrual cycle (by convention, the first day of menses is day 1 of the cycle, even in girls with irregular cycles). A complete blood count and coagulation tests are standard.

It is important to first exclude pregnancy, and next, to distinguish between ovulatory (cyclic) and anovulatory (acyclic) DUB. The differential diagnosis varies accordingly. For example, DUB is the most common cause of excessive menstrual flow in adolescents with anovulatory bleeding, whereas blood dyscrasias and structural anomalies (e.g., polyps, fibroids) are more common in those with ovulatory bleeding.