Which lab test should be ordered first for a patient presenting with dysfunctional uterine bleeding (DUB)?

In the context of dysfunctional uterine bleeding (DUB), the most appropriate initial lab test to order is the serum beta human chorionic gonadotropin (HCG). This is crucial because one of the first considerations in any woman of childbearing age presenting with abnormal uterine bleeding is to rule out pregnancy. The presence of HCG in the serum indicates that the patient is pregnant, which can significantly alter the management of the bleeding and provide insight into any potential complications, such as a miscarriage or ectopic pregnancy.

By prioritizing the serum beta HCG test, the healthcare provider can quickly determine whether the source of bleeding may be obstetrical in nature, which requires a different approach than other potential causes of DUB. Once pregnancy-related issues are addressed or ruled out, further tests, such as a complete blood count or additional hormonal studies, can be ordered to evaluate other possible causes of the bleeding.

In this clinical setting, understanding the potential urgency and implications of pregnancy status allows for timely and appropriate management of the patient, which is why this lab test is of utmost importance in the initial assessment.