Diagnosing primary amenorrhea (the absence of menstruation by age 15 or within three years of the onset of puberty) involves several steps:

1. Medical History: Gathering detailed information about the patient’s menstrual history, growth patterns, and any signs of puberty (such as breast development and pubic hair growth).
2. Physical Examination: Assessing physical development, including checking for secondary sexual characteristics and any signs of hormonal imbalances.
3. Blood Tests: Measuring levels of hormones such as follicle-stimulating hormone (FSH), luteinizing hormone (LH), thyroid-stimulating hormone (TSH), prolactin, and androgens to check for hormonal disorders.
4. Imaging Tests: Using ultrasound to examine the reproductive organs for any structural abnormalities. In some cases, MRI may be used to check for pituitary or hypothalamic disorders.
5. Karyotyping: Analyzing the patient’s chromosomes to identify any genetic conditions, such as Turner syndrome, that might be causing the amenorrhea.

A comprehensive evaluation by a healthcare provider, often a specialist in reproductive medicine, is essential to determine the underlying cause and develop an appropriate treatment plan.