No single test can diagnose PMS. A diagnosis of PMS or premenstrual dysphoric disorder (PMDD) is usually based on a medical history and information from a two- or three-cycle menstrual diary(What is a PDF document?) where you record your symptoms, menstruation days, and ovulation days, if possible.
It's important for your doctor to rule out other conditions that cause symptoms like those of PMS, so it may take more than one visit to diagnose your symptoms. Diagnosing PMS may be difficult if you have another condition that gets worse during the last 2 weeks of your menstrual cycle.